It wouldn’t surprise me if she was told that. I know a number of morbidly obese people who were told to stay off treadmills due to the risk of injuries. Some after developing shin splints, one after a fall. I myself, and my BMI is <25, was told no treadmill work EVER after being diagnosed with a navicular fracture that is now screwed together as best they could. For me, it’s bike, shank’s pony, or pool work only. Treadmills are harsh on the feet (and knees) and people running on them have to keep pace with the machine. At least going for a walk outside, people can go at a pace that is comfortable for them, and they’re unlikely to fall off the back.
Anna should not be using a treadmill, but she shouldn’t be running/jogging either.