Ask her which interracial video she likes to the most. That will give you insight into what kind of guy she likes. Then, watch it with her. Pay attention to the guy, what he says, how he acts, how he fucks etc. See if you can find more like that. Be him in bed and tell her to imagine him, not you. Also, it sounds like she is doing it for you but not really for herself. So, why not get her to talk with some other white women online who love black cock. you know, the ones who can't say enough good about black men.
One last secret weapon: Tell her you want her to think about the hottest guy she can think of and to imagine that she is fucking him ---not you. Tell her it will really turn you on and that you want her to call you by his name while she is fucking. Also, when she cums, tell her to scream out his name e.g. "i'm coming _______!!!!
This will eradicate any fear she has of losing you because she wants to fuck someone else. She will come super hard since she's thinking of the guy she really wants to fuck. Also, ask her to make you someone else, every time you fuck. She should always imagine someone else, who is totally hot to her, even a woman, it doesn't matter. Show her that you have no ego and only care about her pleasure. Tell her you WANT her to be selfish and think only of her sexual pleasure when you're in bed. Tell her you want her to tell you what to do and how to do it and that you will obey her every command. Even if that command is to act like a stud, etc. It doesn't matter. If she tells you to lick her ass, you will do it without question. Once she understands that her pleasure is all that matters, she will feel freer to do things on her own. Making her Skype is a bad idea because you are control.ing her. If you will give up control to her by letting her understand what only she matters, things will rapidly change.