I find myself commenting on a thread that I first commented on 6 years ago. If you're new here, legitimately looking for advice, please give my answer in the first line of this thread a view. I was very fortunate in taking what I feel to be the correct approach with my wife very early in our relationship. It worked incredibly well for us, at least.
Everyone is different, some people are not anal erotic and you may never be able to change that. However, I'd say I believe it to a big mistake to attempt to introduce anyone to erotic enemas as a treatment for constipation,. You're beginning with an unpleasantness, very difficult to turn that around into something sexual. I've loved enemas for decades, but find nothing arousing if using one because I don't feel well. Better to approach it as something pleasurable with your partner from the begining. Being attentive to your wife's pleasures will put you in the best position to introduce her to anything new, or outside her sexual norms. Of course, there is still a chance she may not enjoy receiving no matter what you do, but at least, if you've attended her well, she will be far more likely to administer to you knowing she's pleasing you. Nothing turns my wife on more than my moans of pleasure/letting her know how much she pleases me.
If you're younger/in a new relationship, you may have the good fortune of finding that your partner has never had an enema, and that can be to your advantage. Too many people have had, in their past, a very unpleasant enema experience that the memory of which would be hard to overcome. We're not young, but we were when we met, and despite the fact that enemas were not an unsual household ritual back then, my wife had never experienced one. So she had no preconceived notions. She'll say now that enemas have never been anything to her BUT an erotic experience, and she regards the equipment we have in the same way she does any other sex toy in our toybox.