I'm with Blueberry on this one. Gotta try to save everyone. People do bad things, but that doesn't make them stop being people. (The memetic "best girl", for instance, is a murderer that uses human souls as the equivalent of cattle fodder.)
Giving up on someone, for crimes they might commit - when we already have argued for Oriko and Kirika's sake against Homura - is nothing more then hypocrisy, and an easy way out.
Even if it's hard, and makes things difficult - I don't think trying to help everyone we can could ever be wrong.
Hell, even just giving her friendship and support might help. Even if not...at least give her a warning, about exactly how horrifying being a meguca.