OMG.. She sounds horrible. You already had a bad vibe about her, and that night she didn't prove you wrong.
I would suspect that she has always been secretly jealous of you and that was her opportunity to put you down... (disguised as abit of humour of course).
I think I would have been taken off guard and shocked by this behaviour. Nobody expects this behaviour. I think you should take this to HR because this was still connected to work.
To be honest, her behaviour does seem to have narcissistic undertones. Going in someone else's bag shows a complete lack of 'boundaries' ,'entitlement' and 'arrogance'.
Laughing at you shows lack of empathy. Twisting the whole situation to make it seem like a joke is highly manipulative. These are narcissistic traits.
It's not a joke, she was clearly belittling you.
Putting you down would make herself feel better and she could gloat at your reaction.
I wouldn't be surprised if she is disliked by most people where you work.
I have met people like this over the years. I work with someone who has a similar nature. I avoid interacting with them as much as possible.
Even if you confronted this person about this, I reckon they would just deny, minimise and blame, or make a big issue about something you did, or your tone of voice in even speaking to them about it, just to avoid accountability. This has been my experience with people like this.