As anyone who knows me can attest, I am no expert on this type of thing, but my vote would be NOT to ask her about what was going on.
I’m not totally sure what was going on back in December (and from your post I guess it wasn’t totally clear to you either). If this woman was your girlfriend–i.e., the two of you were dating exclusively, she had clothing at your house, the default was that you went out together at least one night each weekend, etc.–then it seems to me that a 6 week absence is a long time, and both of you need to talk about what happened.
OTOH, if this was somebody who you had maybe been out with once or twice, then I would not go in for a big discussion about anything.
To use an analogy that I may get flamed for, it’s kind of like you are trying to sell a car. Let’s say 6 weeks ago someone came to look at the car, and seemed interested, but then you didn’t hear any more from them. Let’s say it’s now 6 weeks later, and you still have the car for sale, and the person calls you up and says, hey, do you still have that car for sale? I would not advise saying to them “yeah, I do, but first, where were you for the past 6 weeks? I thought you were interested and then I never heard from you, what’s that about?” Instead I would say, “you know, as a matter of fact the car is still for sale. I’ve been really busy lately so I haven’t had time to sell it. If you’re still interested, do you want to come by this weekend and take a look at it?”
In other words, I think the first question is for you to decide if you are still interested. If you are, then just take it casually and pretend like nothing (or not much happened). You can just say, hey, great to hear from you, it’s been a while. Do you want to get together for dinner? (or some such).
One danger to watch out for: people like to have other people in orbit, and email is often their medium of choice for keeping others in orbit. They can send somebody an occasional email (often just forwarding them some joke or link or something) with little effort, but when it comes time to actually spending time with the person, they aren’t that into it.
What do they get out of this? Well, like I said, they can feel like somebody out there is into them, and they get the ego boost, and they also feel like they are keeping their options open.
I guess what I am saying is, if you are still interested in this girl, move the situation as quickly as you can to the point where you are actually spending time together, not just emailing headlines from the Onion back and forth for the next 6 months.
Constantine