You guys are all missing a very important aspect of this, and that's in the question being asked.

I would say "This is her", and so do most people that think it just sounds right, because it sounds right for good reason.

The point is, when someone asks something like
"May I please speak to Jane?"
when you reply "This is her", the 'her' is talking about Jane from the question, and you could just replace Jane with her and it still makes sense "May I please speak to her".
You wouldn't say "May I please speak to she."