1 - There's a very good possibility this is true, since I myself have known similar situations with friends, some worse then this.
2 - If they started at 17, and she is now 19, telling her bf she likes it more with her dad, it could possibly mean that she WANTS it to happen, and being that she has reached a mature age where she cannot be told by the "law" what is or isn't illegal, it must be made clear that she has obviously made her choice, therefore, let's all stay open minded.
But this is also where I could find the possibility that there is a problem.
You means, her fathers will is the law!!!!
There MIGHT, and I say might because I'll try to view this from every possible angle, a form of abuse in this situation. Could it be her father, when this began, uses his "god" status at home to claim his daughter? Very possible, could it be through psychological intimidation she has submitted to him and likes it ( let's take the fact that he seems big enough to please her ) ? Yes very possible again. You will not know until you sit her down with a professional who will dissect her brain and get to he root and truth of the matter.
No moving on to you, it's quite clear that your small penis, your past female role playing with other boys and gay activities, along with your quick submittion to your gf makes you a born and bred sissy. It must be encoded in your genetical structure. I say if this is real, it's a great match for you