Problem in the girth area

[WDF]

My mare has what i can only describe as a "puffy swollen lump" in the girth area; I initially thought it was a girth gall (even tho we'd never had one before) so have stoped riding her and started cold hosing the area twice a day, it went down loads then i lunged her with a roller on - it came back up again :confused:

I stuppidly looked on the net last night so now think we have some nasty evil sarcoid or an oedema; vets coming out monday but do you have any thoughts?