Unfortunately, a lot of young girls in college seem to go thru this, I think because they are dating guys that even though are their same age are emotionally immature and don't know how to deal with rejection. It reminds me of grade school when I was the nerd and everyone refused to sit by me.
I am sure that a restraining order is going to give the boy the idea, and I praise you for being proactive. No one needs to listen to demeaning language. Unfortunately, without a direct threat, I don't think the police can do much.
But you can certainly encourage your daughter to learn from the experience. For one, listen to instincts, when it isn't right break it off and don't drag it out. Also, stand up for herself. She can block him from her email and phone and tell him she is calling the police if he ever does that again.
It sounds like you are doing a great job as a long distance mom, and even though she is having a hard time, and the situation sucks, the bright side is that she reached out to you for encouragement and insight, so you are doing something right!