I think that she is entitled to do whatever she wants to in the privacy of her home, not in a place where if she falls on her face she will sue for improper supervision. In regards to the ignorant comment about treadmills being an excuse for people allergic to exercise, I will remember that next time it is snowing and 10 below and cannot go outside to do my cardio. "Allergic to exercise" my a**
Suffice to say that I have seen plenty of people out running on cold days. I've seen heaps of people out walking on cold days. So yes the people on the treadmill are allergic to exercise.
I can see a place for cardio machines, but don't try to pretend that that is how they are always used.