Hiya!
Simply put: You're the GM, not the Player. It's not your "job" to bend reality and over ride what a Player chooses to have his/her PC attempt/do. You simply adjudicate the results of said action.
Now, if
I was a Player...I'd never trust Alissa again, or at least not without a significant show of change and regret. I mean, at that point everyone 'knows' that if Alissa is ever in a position where its "her or you/them/me", then she would have no qualms about doing whatever it takes to save herself...including knocking me unconscious, then killing me on purpose so as to 'tie up loose ends' that might make her look bad (re: I survive and say "Yeah, she tossed a grenade for frac sake!".
It
would make for some interesting party dynamics, however, so that's the bonus.
So long as Alissa's player isn't of the "I can do what I want because it's what my character would do...and you aren't allowed to hold my PC responsible for it or do anything against my PC" types (we all know those types...! ).
^_^
Paul L. Ming