Post the photo. She's probably in heat, but may have a vaginal or uterine infection, which would require veterinary care. And if she is in heat, that probably means that she either already did or is shortly about to get bred by the stud that's in the pen with her. Which will require a shot of lute from the vet to abort, as otherwise pregnancy could easily kill her at her young age and tiny size.
Edit: I see the image is up. Don't really see anything abnormal there. Is there discharge? I would still absolutely have both her and the other filly checked for pregnancy.
Last edited by bubba13; 12-04-2011 at 06:52 PM.