It could be dehydration? If you start noticing lots of sharp-crested wrinkles around the bends when she balls up, that's probably what it is. I don't know much about it myself, but @wheremyscalesslither on tumblr is a pretty good resource for this kind of thing. I linked to a search for their info on dehydration, so you can look at some pictures and see if you think that's it.

If it is, or if you want to treat for that just in case, there's a "sauna" sort of thing you can do to help. Here's a link to brief instructions on it written by @i-m-snek, and how it should look from the outside. That specific post is directed toward helping with stuck shed, but the principle is the same either way. In case the links don't work:

Take a plastic tote, the kind with the locking lid, and drill some small holes in the top. Put in warm water (90 degrees F tops) up to about a quarter inch, put the snake inside, and lock the lid.
I've also seen others put in a damp towel for an "island" so that the snake can be in the humidity without necessarily being in the water, if that makes sense. The sauna should be about 10 minutes at a time, no longer than 30. You can always do it twice a day if you're really worried.

Like I said, I don't know much about this myself, this is just what I've gathered from others.