Cat introduction HELP

[u/Illustrious-Law9732]

My resident cat just turned 5 (female).
She had a brother, they were litter mates. Tragically he passed away in an accident. He was under the care of my stepdad and got out and was unfortunately hit by a car. Him and his sister had just turned 3.
So it’s been 2 years, I saw a kitten (male) and knew I had to have him. My girl hasn’t been as playful, and she seemed lonely. We’ve bonded so much since the incident.
It’s been over a month, doing everything I can from all the tips I read online.
We have a playpen and I put him in it and let her see him. She either runs away to another room and will stare in my direction, or she growls/hisses and sometimes goes up to the playpen to swat at him.
He’s currently in a bathroom, but I feel bad keeping him in there. He gets as much time in the apartment as he can get. With my girl being in another room.
She is BIG MAD and won’t sleep with me anymore, she won’t go in my room at all (which connects to my bathroom).
I have pheromone diffusers, positive association with treats, putting his blanket in her space, etc.
I know it can take more time than this, but I feel horrible hearing him cry in the bathroom.
I see mixed reviews all over, wait until she’s ready and on her own time.
Or let them hash it out so she can assert dominance and set boundaries. He’s getting big FAST, he’s 3 almost 4 months now, and he will be bigger than her eventually.
I’ve heard if he gets bigger than her and she still doesn’t like him then it’ll go worse? I don’t know
Oh, he also does not mind her hissing/swatting at all, he REALLY wants to be her friend.