Does this make me ?

My girlfriend and I have been dating for several months. She is on the track team at our college and I am just a regular student. We are a good, healthy, in-shape, and good-looking match for each other. And the other day we went to the beach. Afterwards, she asked me to do something new. When we got home, she asked me if I would orally satisfy her from a different postion. What she meant was for me to orally tend to her "cookie" while she was on all fours and my head was buried up in her tooshy. She was still nice and warm from the beach, when we got home, and when I took her bikini off and got my nose buried up in her bum, I found that I really liked how she smelled back there. I could smell her bum and I liked it. And I liked how her "cookie" smelled in conjunction with her bum's scent. What does this mean? Should I tell her about it, or keep it to myself?