This is... mostly speaking from experience. But the type of ability I have? *they make a flame appear in their hand for a moment to demonstrate, before making it vanish*

The energy that's needed for this builds up naturally inside of me. Eventually, that energy can get to be too much, and it can cause a backlash. While I don't need to use my ability all of the time, I need to use it in some form almost every day to avoid such a build up.

It's very likely that in her case, something triggered for her ability to awaken, but because she didn't know about it, or her instincts said there was no need to use it, it started to build up, causing her headaches.