That's what I wanted to post basically. I'm still engaged and not married yet, but I did ask her father. She knew how I felt about it and that I'm not going to "ask someone for the permission to marry you". But prior to my proposal she told me, that whenever I'll do it, it would help her a lot if I did it before proposing. Her parents are somewhat traditional and with us being a transatlantic couple, my proposal would've meant that she moved from the US to Europe. She was terrified of telling her parents herself, fearing that they may not be amused about my proposal. But I let her know, that I will propose to her, no matter what the parent's reaction will be. I once read a very, very accurate and good quote (I think it was by a user of reddit) in case the parents react negatively: "I'm asking you to join our family, I'm not asking for permission to join yours." That perfectly summed it up how I felt, and if he would've reacted negatively, that's what I would've told him.

So in the end I did it for her, to make it easier in case her parents would have a negative reaction which could've been very hard for her to handle. But no matter what they would've told me, I wouldn't have changed my plans. That said, going to be married next year and still very, very happy about my parents in-law :)