actually we had anal a week ago and she enjoyed it for once, i just went really slow for about 20 minutes messaging her anus with alot of lube and then used my finger to get her used to it. at the same time i rubbed her pussy to make her wet and even more horny. it worked!!!!
Anal sex needs a very good preparation, IMO it should be kind of celebrated. Start by giving her an extensive "russian oil massage". That means you massage her anus with your oil-soaked fingers. This way she'll relax, maybe you can even make her cum...
Hope this is helpful. Enjoy yourselves! Drop me a line of you like.