My Mom Is 81, She Has Always Been Thin, Approx

My mom is 81, she has always been thin, approx 115 lbs, 5"8". She is tough, still can work, clean, garden etc. A couple of months ago she has a tingling and pain in her toe (later she said it felt like shingles pain) then her toe was red, then it went away. Then her foot started to swell, her calf and up past the knee. She has seen 5 doctors including a foor doctor. It is only one leg. Working doesn't make it better or worse, resting with it up doesn't reduce the swelling or pain. It is slightly red and slightly hot. They gave her antibiotics, it didn't change, They dais they can't see a blood clot because it's too swollen or a cyst or tumor. She is miserable. She has always been active, eats well. SHe's tried a pressure stocking, that was agony, she's tried ice and heat. Any suggestions?