Where in that do you read her doing anything wrong?
From your own words:
and tries to stop him grabbing his drink
...
Likely she can tell he’s about to get violent
He hadn't yet committed a violent act. There was no indication from his posture or body language that he intended to commit any violent act. Any potential violence from him wasn't yet "imminent", which is a requirement for the use of force in self defense. Taking the glass wasn't justified; it was instigating.
