It depends how you want to watch her. I can keep basic watch on her without risking being caught. Where she is at any given time, if she does anything dramatic herself. That sort of thing.

[ The problem is that the older, cleverer vampires tend not to do things themselves. It's all traded favors and social influence. Things that are either risky or impossible to track. ]

The more traditional kind of watching her, with the mirror or otherwise- I wouldn't recommend it. A vampire her age wouldn't have any difficulty controlling what the mirror shows of her. It'd be nothing to give us false information and then catch us out when we act on it. Finding someone else who means to watch her and getting information out of them might be an option - we can't be the only ones who are wary of her.