Now wait a minute...
"I mean if it's only for a sec than I don't know why it is such a big deal for her..."
It may not be only for a sec. I had really bad pain my first time and for a few days afterward. And why shouldn't it be a big deal? It's her virginity for God's sake!
"I have to tell that she's a prissy girl and sometimes she's a bit whiny for my taste"
Why do you have to tell that? I think maybe you suspect that the reasoning behind her pain is that she doesn't really want to do it...And if you're still pushing her, you're a cad.
"but I mean that's the girl I wanna be with definitely if there wasn't this bit of a problem between us!"
"If" there wasn't such a problem? You should want to be with her whether or not there is a problem like this if you expect her to give up her virginity to you.
I hope it's just your choice of wording that's sounding suspicious, and you're not just out to get her to give it up and then dump her.