I was facing the same dilemma with my man, he got a kick out of large dicks, even though he was large himself. He wanted to see even bigger guys fuck me. I need to be really horny and a bit tipsy or more to let go and all has to go slow. I am also into anal sex and there we were after a while able to let really big guys to enter and do me hard. In any case, take your time, she knows what you like, now don't push and let her move at her own comfort level. Have fun you guys