I'm thinking a liiittle more detail on the internals of the rectum would help? It's hard to do without color, and I know that would mean a longer investment than what you typically do with sketches. But it's a thought.

Thanks for the Picture! :D
I like it, but if you're not satisfied you can always try again.
Just fix her posture or angle if it feels like repetition.
I'm sure you can get it drawn to your satisfaction.