All I'm gonna say is that part of the reason she sounds like she's enjoying this so much is that dude know what he wants and doesn't let her say no. She might be looking for a firmer hand then you've been giving so far. For all we know, she was willing to let you creampie her first, but wanted you to just kind of roll her over and jam it in instead of begging for it.
Be more assertive. You both might like it more then you've got right now. And yeah, take that anal cherry first, bro. You can't let this guy have ALL her firsts, you've the one that's been dating her longer.