Try warming her up with a small plug or your fingers. As far as lube is concerned, a silicone hybrid is always a good choice. Sliquid Sassy is great for anal (though not a hybrid). Stay away from any desensitizing lubes or creams as it could lead to rips or tears. It's a slow journey for some people, you just have to be patient with it.

If she's not relaxed, you can use all the lube in the world and it might still cause her some discomfort.

Try using your fingers first and then a plug. Engage in some foreplay and make sure she's aroused before going for it. Using a good lube is important. I like silicone lubes because you don't usually need to reapply, but a thick water-based (like Maximus link) would work as well. You might need to reapply if you're using a water-based depending on how long your session lasts.

Go slow, don't just shove it in there and pound away. Follow her cues, make sure she's comfortable, and quicken your pace only when she's ready for it.

Make sure she knows you won't be upset with her if she needs you to stop, and if she's experiencing discomfort, you should. Anal often can feel a little weird, but it should never cause pain.

Just take your time and make sure you're both relaxed and enjoying each other!

Thank you both for your input. Every little bit of info helps. We've been working on our communication and it really seems to help with not only our sex life, but our relationship in general.

Like PropertyOfPotter said, engage in foreplay first is a must, better yet, let her have a clitoral or vaginal orgasm before anal play/sex. When she is fully aroused, her anal sphincters will be more relaxed and receptive to penetration -- please make sure your nails are smoothly trimmed if you're using your fingers!

Biggest trick to figuring it out... EVER...

She needs to push out like she's having a bowel movement! If she's "trying to pull in," then all she's doing is tightening the sphincter that much more and making the discomfort (or even pain) worse!

Most people never think about the fact that it's like a one-way valve in some respect. It's got to be in the open position for things to work right.

I definitely agree with the trend here - LOTS of foreplay with finger and toys to "warm up", and use TONS of lube!

Another suggestion not listed here: My boyfriend and I use medical-grade latex finger cots (like condoms for your fingers) for both me and him. Sometimes, the drag of a nail or knuckles can be painful inside. Using the finger cots, we get a slippery smooth feeling that really helps!

In addition to finger cots, you should also try using your tongue a little. Not only will it lube up the area a bit, but it'll cause bloodflow to her lowerbits, which might help her be a bit more receptive.

Did you try with your smallest fingers first?