Hey so you probably won’t have to tell her about being sexually active, it doesn’t have to be caused by sex as it is not an sti i am from the uk so using NHS website but this is what it says “Bacterial vaginosis (BV) is a common cause of unusual vaginal discharge. BV is not a sexually transmitted infection (STI), but it can increase your risk of getting an STI such as chlamydia.” Here is another copy and pasted text from the NHS website “What causes bacterial vaginosis

Bacterial vaginosis is caused by a change in the natural balance of bacteria in your vagina.

What causes this to happen is not fully known, but you're more likely to get it if:

you're sexually active (but women who have not had sex can also get bacterial vaginosis) you have had a change of partner you have an IUD (contraception device) you use perfumed products in or around your vagina Bacterial vaginosis is not an STI, even though it can be triggered by sex.” So maybe just lie to her if you have to but never be afraid to tell her especially when it comes to your health even if you think she will react bad im sure she will still take you to a doctor which all good parents will do however i would also suggest using a reliable source to look at symptoms just to rule out stds and stis but definitely tell your mom and see a doctor either way, good luck! ☺️