Puppy training question?

[Jess]

My friend has a weimaraner puppy and has had some recent struggles in potty training her, so I was hoping that I could get some new advice. She is 6 months and just got fixed last week, and that is when the troubles began. Although she was mostly potty trained before he got her fixed, she still would go to the bathroom inside once in a while. I have heard a lot that weimaraners are hard-headed and hard to potty train, but I'm wondering if that's really the issue here. Just this week, she has peed on the couch, his bed, and in his car, which she has never done before. At first I was wondering if she was marking, but he said it just started, so there should be no reason for the sudden need to mark in the house. Is there any way that her getting fixed could influence her bladder? It doesn't sound like a UTI either, she's not having to go all the time. Any ideas would be great! Thanks!
He's asked the vet, and I guess the vet just said that that breed of dog is difficult to puppy train, but I'm wondering if that's the real reason.