The vet called: the mass was a lipoma, NOT the c-word! Yay!!!!!!
I changed her into this long-sleeved t-shirt because she managed to wrangle her leg out of the first one (I suspect rolling was involved). We were calling her Amelie Mae and Marcel-lulah (Marcel Marceau's got nothin' on her!)--all she needed was a little red kerchief, oui? Adorable (said in French accent). Alas, the sleeves wouldn't stay up, even with pins, so she's in yet another shirt (a kids' shirt this time--more pix to follow, of course!).
Thank you all for your kind words and good thoughts--it certainly helped! (And have I mentioned: YAY-o-YAY!) She's on the mend, for sure.