Girl feels afraid of all relationships because of parents history

So this girl I'm on and off with basically says she is afraid of relationships because she's at the point in life where the next one might be the person she ends up with for the rest of her life.. she's terrified and psychs herself out because if she sees one flaw or red flag, she runs- she thinks mainly because her parents split up and they have a terrible relationship. Absolutely hate each other. And she is afraid of that happening to her. She wants the person she ends up with to be the only one and have it work perfectly.

I understand this and am trying to help and show I would never be like that, but it's a fear she hasn't been able to get over for years. (Other relationships too not just me) Any advice on how to handle this? Both my end and her end?