When I was 17 I had a falling out with my mom over the person I was dating. I ran away from home as well. As time went by I got into another relationship that my mom didn’t like and as a result she didn’t go to my wedding and prevented my younger brother from going as well. I am 52 now and as time has gone by I have since mended fences with my mom but to be honest, it will always hurt that she wasn’t there for me on one of the most important days of my life. So from my experience I would say that you really should go to the graduation and really try to convince her dad to reconsider. Even to just sit in the crowd and watch without interacting if he prefers. Problems like this will eventually be resolved but the hurt she will carry by you not being there will never go away even after the relationship gets back on track. As far as the boyfriend goes she is so close to 18 that trying to cause issues there will only push her further from you and closer to him.