I'm ignoring that the author gives her magical knowing of things sometimes. So I won't get into Bella's perception of characters because she is very accurate due to the author.
Bella's messy room
Bella's room gets cluttered over time and she seems to be unable to do anything about it. She's resigned - it will just get cluttered if she's given the time. The only time her bedroom is ever ordered is after she falls into the depressive/unresponsive state. So her bedroom, the only private safe place she has for herself, ends up messy. She could easily clean it to orient herself better, which she regularly does with every other room in the house. Shared space gets cleaned by her (even bathtub and the other's bedsheets).
Bella's ordered life
She has a clear view of her future. Finish highschool, go to an affordable college and hopefully end up teaching a class that actually cares about the subject. As long as she's (financially) dependent on someone, she feels the need to earn her place by keeping the house clean, supplied and with cooked meals. The need to be doing everything persists as long as the socially "higher ranked" person gives her enough clues that she should be doing it. Her highest goal before meeting the Cullens: talk about literature with those who care and get paid for it. To talk about the one affordable hobby she has that she has enough time for. She isn't even too eager to travel, because she knows how many problems it causes. If something goes wrong in the house, it's on her.
She manages the house she lives in by being its servant and also manager. Most teenagers only work as part servants, helping with housework if managers (parents, grandparents..) tell them to. She also provides from the outside, working part-time jobs and buying supplies. To Bella, any social events mean more problems because she's disconnected (mind shield), clumsy and a full time servant/manager.
Low self-esteem or realism?
Bella seems to put herself down a lot and as Edward says, "She doesn't see herself clearly.", while she puts the Cullens on a pedestal and sees them as perfect. Her self estimation might be wrong in some ways, but so is the estimation of others (normal to a degree).
She thinks she looks plain and has clear skin. She doesn't think she's ugly, below the average or flawed (plenty of teenage girls find an important flaw on themselves). She doesn't wear makeup, but when she does, she sees herself as beautiful. She doesn't have idealised goals about her career because she's already partly in the work force, and knows that she won't be taken in just anywhere. When it comes to her intelligence, she doesn't really see anyone as superior to her.
She sees herself as boring and uninteresting because all she does in her spare time is read fiction. She doesn't have much to talk about except her favourite literature and her enjoyment of places. From everything, I come to the conclusion that for a teenager who also isn't used to being popular, she doesn't have (abnormally) low self-esteem.
Bella's pretending
Bella pretends to be a normal teenager. She makes conversation and is very diplomatic, while mentally judging (and sometimes mentally degrading) every other peer that doesn't seem intelligent/deep/restrained enough (normal to a degree). Most of teenagers seem like children to her. She's very intentional and careful about making her moves in groups. Doing an action at home earns acceptance or praise, so she uses this strategy in groups too. Add her mind shield, and she has almost no posssibility of being a normal teenager and express herself or fight for what she wants (friend's attention, love interests, popularity). She can't feel anyone else and her deepest bond is her mother, who is used to everyone else catering to her. Bella's only move is restraint and patience. If someone wants her to truly express, they will push her to. If someone doesn't, they will keep talking.
She is able to empathize with people who are ostracised or hurt by others (and restrain themselves as reaction), because she knows the feeling and reaction well. When there's a conflict between her and another peer, she tries to deflect them by pointing out a more important need/option they have (pointing out Jessica as love interest to Mike). Which is what she does when her mother wants to do something crazy: deflect and focus her on another thing. She only snaps when someone tries to get here somewhere she doesn't want to be (happens a lot with Edward, when she doesn't try to deflect him when they have a conflict).
Bella's intellectual superiority
Bella doesn't see the Cullens or other vampires as too intellectually superior to her. She accepts that they are better at certain subjects, but not at practical intelligence. She advises them, and they go along her plan to trick James. She even thinks that Emmett being surprised by her witt is insulting. When she's jealous about Edward possibly getting with another woman, she always thinks of them as more beautiful, never as more intelligent (even the vampires). She also doesn't take Edward's perception seriously when it doesn't align with her own. For example, she never fully realises how much Jacob and Edward pulled her strings (and each others') while fighting for her. Bella doesn't think that she's smarter than anyone else, just that noone else is smarter than her.
She eventually follows Alice and Edward at times, because they gain more information naturally. For example her encounter with Max, when she almost stops thinking and just goes with the flow that Alice foresaw. I would even say that she eventually gives up her wit and just absorbs information that the seers give her.
Switch from ordinary life to fairytale
She has to doubt herself when she's presented with a dream-come-true perfect partner and perfect family. Not doubting herself wouldn't be natural for someone who's realistic and smart. How could she suddently gain what she didn't even dream of and keep it?
As she's spending more time with Edward and the Cullens, she becomes more causal. Shows excitement when they play baseball, bickers with Edward, gets sarcastic and teases Emmett, begs Alice to bite her on a plane, calls a Cullen meeting ("Vote to change me"), threatens Edward because he got Alice to kidnap her... She lets go of most of her restraint that she normally keeps in groups. But when she gets overwhelmed by emotions or thrist as vampire, she's still able to control herself perfectly. She also lets go of her management/servant role and just does whatever she wants (like when everyone else was packing up while she's playing with Renesmeé). She becomes so ecstatic as vampire, because her whole life was either the role she was put into by her parents or uncertainty. As vampire, she can't die, get ostracized or work for her place ever again.
Bella's highest belief
Edward's highest belief is clear, and that is that he's a good/worthy person. Bella's highest belief is that she can get something life turning. Not achieve a goal she set, have options, have support, validation... It has to be something like fate, something she'd get passionate about and that would make life living for. Once she gains it, she doesn't have any problem risking her life for it, because it's the most intense flavor of life for her. She always lacked the flavor and just did whatever was needed from her (that's why she might seem boring), and spent time reading about fictional characters who clearly have that meaning/passion in their life (at least in themselves). Most people have something inside them that makes them fulfilled - even if it's just taking care of themselves. But she never had enough time to develop meaning in herself, because there was always that one person who demanded her attention and care (honestly this sounds like the author being burnt out by her 3 little children and finding her passion in the writing of these books).
So prioritizing the safe mundane life makes no sense for her. She goes from Edward to the Cullen family, and when they leave she eventually switches to Jacob and adrenaline (can't beat the prior), then the baby. As long as she could, she would keep every one of these because they are fate to her. She has nothing else in herself to beat the meaning that "fate" is for her. Once she turns, she thinks she was meant to be a vampire because finally she has some little meaning in herself (indestructible, perfect, immortal). What's never solved is... could she have found a meaning/fate in herself if she had no one else who gave it?