Well, she seems to have an alibi. Also, she is too ordinary.
Not really, necromancers fight remotely though remote control. So even if its known were she was, which it wasn't really expressly stated to be the case, she could still be controlling undead to do the work from afar. So a alibi wouldn't really clear her.
That said I dont think its her. Though it is odd how the series is handling her, she is outright using a forbidden power yet no one is batting a eye or persecuting her for it. That no one has addressed why is she being allowed to use necromancy is odd. Though feels like bad writing so the author can make us think she is Hollow by delaying telling the reason why she is allowed.