Ok, Kiddo... First of all, don't forget to breathe. *chuckle*

Now, it is nigh-impossible to figure out whether or not she'd be interested in being more than friends with you based on her actions and these dance-around-the-topic conversations you two are having. I suspect after that online conversation that she might be interested, otherwise when you semi-joked about the 2 of you going on a date, she would have just blown it off or changed the subject immediately. The fact that she asked could be a good sign.

So here's my advice: Instead of asking her straight out if she's interested (straight-forward is often a good thing, but it has it's place!), just say something like:

"Why do you think you and I have always been just friends?"

This way you are asking the question, but without revealing that you wish it were more. If she doesn't feel the same way, she'll be able to gracefully answer without putting something weird out there in the way of the good friendship you have now.

A) She might say something like, "We just don't think of eachother that way." or "We wouldn't want to mess up our friendship." This is her way of telling you she's not interested in more. Go to D.

B) On the other hand, she might say, "You never asked!" or "I never thought you would want to." If so, this is your opening. Continue in the hypothetical, and say something like, "If I had asked, would you have said 'Yes'?

If she says she would, then it is time to make your move!
If she says No, you have your answer - Go to D.
If she says "I don't know," skip to C.


C) She might just say, "I don't know." Then you can ask her if she's ever thought about it.

If she asks, "Have you?" go ahead and admit it! But be casual and light about it: "Of course. We get along so well, and you know you're beautiful - I'm a guy! Of course I have thought about it."
If she says she's never really thought about it, back it up - She probably doesn't want things to change. Go to D.

D) Be prepared with something upbeat to change the subject so it doesn't get too heavy, like, "Holy shit, did you watch South Park last night?"

You can do this! You'll find out what you want to know without fucking up the friendship.

Good luck!