That sounds a lot like weak snick. It can be cause by mechanical problems with the trigger (say, getting a piece of sand logged there), or by an infection of some sorts, such as ciliates or other parasites.
The first thing I would try is a fresh water dip. Make sure the temperature matches the tank water as well as the ph, and keep her in the dip for 8 minutes. If she thrashes a lot, that's a good sign its parasites, don't remove her early. Only remove early if she seems to stop breathing (and do watch, some seem to "hold" their breath for a few seconds in stressful situations.
Try offering smaller food than normal - if you're feeding pe mysys, get some hikari cubes. Also try live brine shrimp - anything you can get her to eat.
If she can't eat at all, you may need to force feed her. I wouldn't go there yet, as it will be stressful to you and her, but I've done it successfully with a few seahorses that couldn't eat. If you do get to the point where force feeding is necessary, take a look at this article I wrote:
http://www.fusedjaw.com/advancedcare/instructions-on-sedating-force-feeding-and-cpr-for-seahorses/3/ and let me know if you have any questions. The info you'll need is on page 1, 2 and 3.
If she doesn't respond to the freshwater dip after a few days, you might want to consider placing in a hospital tank and treating with formalin or quickcure (I prefer quick cure, but it is more harsh than formalin alone). The only downside is, there isn't a great way to figure out what is causing the problem i.e. physical injury or parasites, so you could possibly be treating for something that isn't there. In other words, proceed with caution.
