Lots of good theories here. Might even be a combination. You might have pushed away a little, but then she may not have been into you enough to really care. As for the reason she texted you now, she might have just felt sad for something unrelated and needed validation. Whatever the reason, don't worry about it. You asked her out, and that's all you can do.
I've said it before, but the only person you should try to understand is yourself. That's not even easy.