My girlfriend is selfish in bed.?

My girlfriend is extremely reserved sexually. While she's agreed to experiment with me on occasion, she mostly refuses my indulgences. I've been trying to get her to pleasure me orally on my anus for a full month now, but she's so selfish that she won't even try. I bought her flowers, chocolates, and some VERY expensive jewelry, but still she shoots me down. I thought about trying the dog, but I'm pretty sure that act would constitute animal abuse. Please note I have NOT tried the dog, NOR WILL I. I just thought about it. What else can I do to get my girlfriend to come out of her shell?