I've had a few like this and IMO, some were doing it to intentionally annoy/hurt the kids but some did it because they didn't know any better, didn't realize that they were hurting and were just basically bulls in a china shop! Lol.
If you think she knows better and is doing this stuff intentionally than I agree that it needs to be stopped sooner than later so that it doesn't turn into more serious bully behaviour. Mom needs to see this as an issue so maybe a 4 week probation would be eye opening for her!