With a 3 yo female acting like that it most likely the 1st season she is showing signs of wanting to breed. There was another similar thread not to long ago of almost the same thing. This time of year she is more than likely looking to bulk up for her first breeding season and I can only say feed her. No matter what else you do it will not stop her from being the way she is right now.

Also you can look forward to her not eating for a period of time, so when that happens don't get alarmed. It is normal. Now get yourself a male to breed to her.

Hope this helps and good luck.