I feel like this is unlikely, based on Vibes from the shapeshifter. She does seem a bit too trustworthy and friendly, but it would be a pretty big rug pull for her to just suddenly go evil, in my opinion
I mean, it might not be sudden at all and might have nothing to do with "evil". The Shapeshifter seems to just be doing her job most of the time, and following the rules:
We just don't really know what that job is or what those rules are.
She also hasn't exactly shown she's actually on Sensei's side. If anything she's implied he isn't supposed to figure things out:
Albeit, that could be what's in his best interest.
I mean she's literally hiding her motives, working with supernatural entities, is a shapeshifter, and knows how to manipulate Sensei's mind to make things happen or unhappen. She's also possibly insane and tried to sell Goat Urine:
and might even be the one driving Nodoka mad:
She's definitely suspicious.
Besides her being possibly Sensei's and Ayane's unborn shapeshifting daughter as a teenager, there's not really much reason to trust her. Any "help" she gives could be simply her job or in her best interest. Maybe both.
