My gram's foot gets red and swollen when she walks. when she elevates it, it's fine. her bloodwork came back normal. she's 86. what's wrong with her?

Foot red and swollen: By excluding, does she get swelling on the other foot? I would say that venous sufficiency could be the first. She will require an ECHO/DOPPLER of the venous system, of the affected extremity. Check for pulses, at the ankle one anterior and one posterior, and on the top of the foot. behind the knee and at the Groin. Rule out osteoarthritis, by doing X rays. Does she get pain? Keep well