hard to say with out seeing it, or feeling it but.....
It could be a lipoma (collection of fat cells) or...
Hematoma (collection of blood outside of blood vessels)...with a hematoma, treat as with....Rest, Ice (cold hose), and compression. She could have gotten kicked, or bumped herself, and you weren't aware, but burst some blood vessels diuing the incident.
Both are harmless, and generally go away on their own, or, remain, and are more a blemish than anything. (hematomas usually go away, but the odd one stays....just isn't as large as the initial bump.
That being said, may want to get your vet out to check to ensure that there isn't anything seriously wrong...more than likely not, but always safe than sorry IMO
Horses are like chips...you can never just have one
Last edited by Maverick101; 11-13-2009 at 02:06 AM.
Reason: spelling errors...again!