I feel so negligent for not seeing it...
Anyway, it's similar to the bumps two other horses had a few months ago.
I guess it's maybe a little bigger than a golf ball. I lunged her and rode her (all before knowing about this lump) and she was not off at all. She was actually fairly energetic from being in all day.
She'll let me touch it, but she slowly moves away, so I know she's not in too much pain. I put some of my veterinary liniment on it, and hosed it before hand.
There was no tick, and I didn't see any blood. It was fairly solid but kinda squishy