Maybe she sprained it? MS is generally a joint thing, if it takes the path of leaking from the tendon sheaths...hence the fluid leaks into the joint and down into the pads. Feel up at the hock...is it hot or swollen?
If none of the joints are effected, then I doubt it is MS. And when it is MS...
Molly, is the foot joint swollen? Swelling at the joint there is classic MS. You will sometimes notice opaque looking scales and they can be raised around any area that is swollen. MS generally strikes the left foot only, from what I understand. There is usually lots of heat and redness with MS...