I must admit that I used to behave like that
Everything my husband (I got married at 22) did that I thought was not acceptable (minor things and many imagined) would become a "how dare he do or act like this if he loves me?". I can't even explain the reasoning behind it all now because I can't even see the world from my own eyes if I look back.
My husband's theory is that I was acting like a spoiled brat and for lack of a better theory he's probably right.
Hopefully your girlfriend will grow out of it and mature.