Well I spent over 23 years 'suggesting' anal play to an obviously very reluctant partner. Now that she finally agreed - it has become almost routine. I'm obviously one that didn't push hard - but in light of the results, it's clear I did not push hard enough.
The biggest surprise to my wife is that she actually finds pleasure in it.
I would do some research on the many anal sex threads on EF and use the enthusiastic comments made by women as proof that when done right anal sex can be positive for both partners - even to the point of orgasm.
After warming up my wife with my fingers and a tapered vibe, I'll enter her (using a ton of silicone lube) and give her a clit vibe that uses while I slowly increase the speed and depth of penetration. About 1/2 the time she will have an orgasm this way.
I also suggest that she do anal play on you. This has 2 advantages. 1st and foremost you can experience what she will be feeling and getting an understanding of the need for - and methods of warming up and the importance of pausing after penetration to allow for the anus to adjust.
Secondly it will show her that you are getting pleasure from it - hopefully from this she relates this to her own ability to both accept anal penetration and enjoy it.
I'd say we had regular anal play and penetration on me for a year before she warmed up to the idea of trying it out herself.