Carla was a violent criminal who belonged in prison

Pushing someone off a bar stool, which she did more than once, could result in serious injury or even death, and even if it didn't, it's still assault and/or battery. She was fond of throwing drinks in people's faces too, which is also assault and/or battery.

On top of that, she was a thief. Off the top of my head I remember her stealing someone's car battery and Frasier's Rolex, the latter of which would almost certainly be considered grand theft. The former could have potentially had serious complications, such as someone not being able to use their car in an emergency situation because a little piece of garbage stole the battery.

I think most, if not all, of the main characters committed at least once crime on the show (Norm stole beers more than once, for example), but Carla was by far the worst.