Of course, it's abuse. Pushing is still abusive physical contact aimed at demonstrating his power and his physical dominance over her and it is probably accompanied by verbal and emotional abuse also. My ex never actually hit me either but he made my life so miserable that I wanted to die!
Of course, until she is ready to get help, there isn't a whole lot you can do. If she won't see a domestic violence counselor, perhaps you could go and they may be able to give you some hints on how to reach her. Many women don't want to discuss it because they are so ashamed - I know I was. After such a long time of being treated this way, they have come to believe that they brought it on themselves, that they are at fault and deserve to be treated that way. Does this woman have children? If she does, you might remind her that they are observing and picking up on all of it. Girls and boys both come to believe that this is a normal, accepted way for men to treat women. And she needs to know that these things follow distinct patterns and unless something happens to ward it off, it escalates. It starts with verbal and emotional battering, goes to physical bullying like pushing and shoving, then will cross over to actual physical battering.
It must be so difficult to watch this happening to someone you care about and not really being able to get through to her. In a bad relationship, I've always heard that a woman willl stay until it becomes absolutely unbearable. A man will stay until he has somewhere else to go (like with another woman). I hope things start to look up for her very soon.