I can't tell you how to fix it, but I might be able to help you see why it hurts in her back. You did spell it right: costalchondritis just means inflammation of the costal cartilage.
The costal cartilage is the (cartilagenous) extension of the ribs to the midline of the body. In the front of the body, the lower ribs do not meet the sternum, but instead, extend a cartilagenous arch up toward the sternum. If you follow your lowest ribs from your vertebra towards the front of your body, you'll feel where it arches up and becomes flexible. Because each costal cartilage is connected to a rib, the pain from inflammation of this cartilage could easily radiate towards the back.
There are many causes for this--someone would have to actually talk to the patient to determine the cause. It could be due to an injury to a rib or to the area below the sternum, or something more systemic that attacks the cartilage--this last option could be all sorts of things.
Her physician should be able to tell her how to deal with/treat the pain and/or when it should subside. Maybe she needs to call and talk to her physician or a nurse at the office. Nurses are usually more available to discuss this sort of thing and are very helpful. i hope they'd want to help her get back to working out.
Hope that helps some--sorry i didn't have more detailed info on how to "fix" it.
Ginger
