Good that you used lube and trimmed your fingernails. That it slid in easily comes in handy and signals that she's able to relax. Which would be all you need going for a physical exam at the docter. When it comes to sex, it's a start, but you're not even half way there. Cause all that matters is pleasure! What does matter is what she felt. Was it uncomfortable, painfull, pleasurable? Was she very relaxed and highly aroused? Also; you say that's all you two did to her anus. Did you warm up before, paying attention to every part of her body before going there? Did you massage it from the outside before going in? Did you involve her clitoris in the anal play?

The anus is very sensitive and touching, licking, fingering and even anal sex could therefor be very pleassurable. See also links below. But it needs to be done with patience and care. Off course things may feel 'weird' and a bit uncomfortable at first, just because you're not used to the feeling. But it really should start feeling pleasurable right after that. If any other feeling occurs such as pain or discomfort, you should stop or shoukd change whatever you're doing, such as going back to massaging from the outside (depending on what feels good to her)

Another very important thing; she should really WANT it. If not, she shouldn't. And she should want it just to please herself, not for anyone else. If not, she shouldn't. If she does truly want it, thing that would be recommendable is her trying anal masturbation. Just like any type of sex, it's good to know what feels good to yourself. Especially with the anus in which concious and subconcious is melted together (given the two sphinxters of which one is conciously controlable, the other is not). There's no fooling yourself! Should she decide at any time that this is not good to her, than that's the line. This could be drawn anywhere; not touching the anus at all, only massaging and licking the outside, penetrating with only very small objects such as a finger, etc. Important for you to remember, dear Ninja, is that this is all about her.

I wish you a pleasurable experience. The more prepared the two of you are, the most likely this will be. So I recommend you two to read:

-http://www.sexinfo101.com/forum/news/29466-ultimate-guide-anal-sex-women... This book gives you everything you need to know for your first experience with anal stimulation (and how to make it a happy one! :))

-http://www.sexinfo101.com/forum/pleasing-him/19950-playing-ball-how-tips... tutorial for people interested in and concerned about the how-to of Anal stimulation as well as play (not just for men)
-http://www.sexinfo101.com/forum/other-sex-topics/29492-help-please.html a little on orgasms through anal stimulation
-http://www.sexinfo101.com/forum/sex-toys-products/28800-dildos-human-anu... on the risk of anal penetration
-http://www.sexinfo101.com/forum/pleasing-him/11220-anal-101-a-25.html with pages of opinions, tips, etc, etc....

-At any time; look through the index, it contains a lot of good articles!