Not really the cardio she's looking for, but perhaps a focus on core strength would be helpful to her running when she starts back up? Most core exercises are either lying down or involve only minimal weight on the feet, so perhaps some sort of ab-focused circuit at a quick pace would fit the bill.

Rope pulls of various types could be a cardio-focused exercise, too-- either those machines that you sit down and basically pull a circle of rope down from above you, or sitting on the ground and pulling on a rope attached to a weight or sled, if you have the space for it.