Swollen Leg, But Not Lame.?

I have a 16 year old quarter horse mare that has clean legs. She now does english and jumps as well! She also lays down 3-4 times a day out side and again at night in her stall. One day, i was doing our daily groom when I saw she had a small lump on her leg where the suspensory ligament is. Its not hot, and the lump was squishy, but after being poulticed, became a little bit harder. She was NOT lame, but was sort of twisting her leg in a tiny bit (you could only see it if you were REALLY studying it, and this only went on for a day or so, 3 the most). I stopped poulticing and ive tried cold watering it 2 times a day for 15 minutes and liniment, but nothing works! My trainer says she probably twisted her leg and caused the tendon sheath to swell, but 2 weeks have ped and the bump has not gone away. When she lays down it the lump doesn't bother her, but when she gets up she favors it for a few strides and is fine again. I called my vet but he is coming out next week to do immunizations. Im going to have him check it out, but is does anyone know what it might be so that i have a clue of what to tell the vet? Thank you!