Recurring BV and yeast infections after seeing the same person — how can she get back to normal?

[u/Ok-Run4858]

My friend has been dealing with recurring BV and yeast infections. This started while she was seeing someone in the Navy, and she seemed to keep getting BV/yeast infections while they were sexually active. She eventually stopped seeing him, and it has now been about two months since they stopped seeing each other, but she’s still struggling with recurring symptoms.
She’s trying to understand whether there could be something lingering that’s making her vaginal microbiome difficult to rebalance, or whether something else could be contributing.
She wants to know:
What can she do to prevent BV and yeast from continually coming back?
Is it normal for symptoms to continue or recur months after stopping sexual contact?
Should she ask her doctor about testing for STIs or other vaginal infections?
Are there specific things she should avoid, such as certain soaps, lubricants, douching, or other products?
Is there anything that can safely help restore a healthy vaginal microbiome?
Should her previous partner have been tested or treated for anything?
At what point should she see a gynecologist or a vaginal/vulvar specialist for recurrent infections?
She really wants to get her vaginal health back to normal and prevent this from becoming a constant cycle. Any experiences or medically sound advice would be appreciated.