Once the inflammation calms down, walking seems to be okay, but she really wants to be doing something that gets her heart rate up and is more of a workout.

Specifically cardio, or would something generally strenuous do the job?

It occurs to me that circuit training with weights/bodyweight can kick one's ass and definitely raise the heartrate, so that might be the way to go -- if it'd be any use, I can raid my notes for all the exercises I found I could do without weighting one foot.