4 Answers

I say just wait. In the meanwhile, show her parents some respect and show the same to her, this will prove your point and your true feelings.................

Her parent needs to deal with it. She's an adult and can make her own decisions. Just do your best to get along with her parent and prove to them that you truly love their daughter. This is between you and your girlfriend. The parent needs to stay out of your relationship. Your girlfriend needs to set her parent straight on this. 

Is there a particular reason they do not like you ?If so you may have to prove them wrong, show them that you are a genuine caring person towards their daughter,  be nice and respectful to her parents.

Tell her parents politely that it'd mean the world to their daughter and you for them to approve the marriage, and to attend the wedding.  Also, tel them know that such is not possible, the wedding would still proceed.