This is where you went wrong:
You never want to be seen as the cause of a rift or exploiting a rift between your girl and her parents -- particularly her father. Once that happens, regardless of the truth of the matter, you will be viewed in an adversarial light. Even if you fail, you always want to make an effort to reconcile her with her parents, because you really don't want to be in a relationship with a girl with unresolved daddy issue. Besides which, by attempting to repair the parent-child relationship, you soften your relationship with her parents, and trust me when I tell you that your chances of having a successful husband-wife relationship are multiplied when you have a healthy relationship with her parents. You don't want to be the guy who "stole their little girl away," and from whom they're always attempting to get her back.
Do it properly, and her parents may even come to prefer you to their own daughter (more common than you might think). Get a chipn on your shoulder, though, and you'll be retiring your spurs...sooner or later. Trust me.
So with this, and i mean this in the nicest way - i approach the meeting, set out how i am going to look after them both for the forseeable and raise no grudges at all.
What if she has told them things that arent neccessarily true? Do i still then continue to apologise and show how I will make it all better?
What im asking is, so how would you approach it?