Saving Mira worked fine for me. You need to be close friends with Cass and Dan of the soccer boys, Mira will ALWAYS be kidnapped (there is no prevention), but you can save her. Go out with Cass, be respectful of time events (meet her outside after school when she asks, talk to her at school to share infos about Mira). You should meet with Simon Banks the PI at the pub so he tells you how to deal with the prostitues, and then tell Cass about it. When you and Cass go whoring, keep selling yourself on the road in the same area as other girls (try not to stay glued to Gingersap/Cass too much), and talk with Gingersap whenever to check on her. After a couple fucks and getting accepted as a whore by the whore community there, you should get like 5/10 infos about Mira, the other infos will be given to you from Cass
That done go talk with the insitute (you don't even need to have done Haven quest or started Curse quest tbf) and Mira will be saved. She doesn't get kidnapped again because Cass will be whoring with Mira every night so they see each others backs
i tried all that, she was in her "casual" outfit instead of her highway outfit, and normally when you meet he she stays there but when i did she vanished again and if i tried to "meet her" again it just kept repeating the "oh wait is that mira" stuff, i tried that on day 4, day 10, day 16 and day 26 all with different stages of friendship lvl and it happened all the time.
(im speaking about the "pepper spray route" btw i saved her once the regular way but it change her and cass's character iirc)