Thumper: You say that she is hugely into anal play. Does that include her playing with your rear? If so, I would try what Michael suggested and try to have her give to you first. Would be less threatening to her, and once she sees how it turns you on she might be more inclined to try, to get some of that feeling for herself.
That is how I got my wife giving to me. She has a lifelong dislike of enemas, due to the monthly ones her mom gave her. She did them very badly, way too much soap and really burned.
But I also knew from her reactions when I would sneak a finger up her ass during intercourse that she is anal erotic. We had never talked about it before, but a few months ago I came right out and asked her if she enjoyed that finger up her rear, and she somewhat shyly admitted that she did. I used that as an opening, my approach with her was that since she enjoyed something up her butt (we have also done anal intercourse once in awhile), what was wrong with me liking mine played with, or having an enema nozzle up there once in awhile?
The way I did it was something you might find useful as well. It is a trick we both have used at times when we have something important to discuss: We write notes to each other. Sounds silly, but has a couple of advantages: The person sending the note has time to organize their thoughts and get them across completely and clearly. The reader can get the whole idea that the writer is expressing, without interruptions or emotional confrontation. Works for us anyway!
Anyway, bottom line (pun intended) is that my approach worked, and she recently gave me a very erotic enema...
Hope some of these ideas help!
Warren