What is this bump on my horse's leg?

Noticed a bump on the outside of my horse's left hind leg about a week ago and I am a little concerned. She was in heat a few weeks ago and got really beat up (as you'll see in the pics) and about a week after she developed this bump..

I believe it's a splint but really would like to see what other people think. I have not been doing my riding with her...just bareback to and from the pasture. She is not lame but it definitely seems to be sore when touching it. It has not gone down at all in the past week. There is maybe a small amount of heat coming from it. I'm just very worried about this being bad enough to bother the suspensory..?

She had splints on both front legs also but those have now disappeared.

I am contemplating getting a vet out to look at her but if this is just something that will need rest I won't worry about it.

Here are some pics that I took yesterday:

http://i1305.photobucket.com/albums/s547/rachelrom...

http://i1305.photobucket.com/albums/s547/rachelrom...

Thanks!