I would say that it is inappropriate to the extent that she was having such a conversation with someone that neither of you really know.

I have no problem with adults talking about sex, it is wise to stay within the bounds of comfort for all involved, but I have no problem with it.

That being said, it is a little odd to have such a conversation with someone you have just met. It would be one thing if it were someone that one or both of you have known for years, but days?

It is great for each of you to have friends, of any gender, and with no worry about if they are a friend to each or both of you. However, there is a world of difference between just having a fun conversation and discussing something that is usually considered to be private.

It is hard for many people to grasp but in marriage the things that used to only be private for you are now private for both of you.

In answer to the comment earlier that said if she were talking about her own preferences, it is ok. The truth is a bit different. In a romantic relationship, and especially in marriage, when you reveal deeply personal things about yourself you are also making that choice for your partner. By talking about the things that you like to do or have done in bed is instantly perceived as your partner being the one who provides or benefits from these things.

Even if the subject has no real bearing on what the sexual relationship between you is really like (maybe the preferences are from times long ago). That doesn't matter, the person your talking to doesn't know that it happened long ago.

The absolute, most important point in all of this is the fact that sex is an act of a couple (ideally). The intimacy, emotions and bonds that are formed through sex are a very private thing. To share this information or ideas about these experiences with someone outside the relationship can stir up all sorts of emotions, many of which aren't even close to good.

Also, not to say that it really has a role so much in this case, something that people should keep in mind is the very real truth of male sexual jealousy. We really are hardwired to respond with aggression if we feel that someone is trying to form an inappropriate relationship with our significant other.

Anyway, I think the best thing to do is to tell her how you honestly feel about the whole thing. Keep it as calm a conversation as you can and explain your side of it. After that let her explain how she feels about the whole thing. Listen to her side of things about what she really revealed, if anything at all. After that you guys can work out some sort of agreement that takes care of each of your concerns.