hmmm, if she's really trying to lose weight, it actually WOULD be better for her to just go on a long casual walk rather than jogging in her condition. Most of your organs, and your muscles too when they are in rest, use fat for energy rather than sugar. If you work at a high enough intensity for you to be out of breath, your body will stop using fat and start trying to quickly burn sugar and protein. Though exercise machines can't really track your breathing so they give guidance for fat burning based on a rough estimate from your pulse. Anyway, if she wants to lose fat, she shouldn't be doing exercises she finds difficult and, instead, do a large/steady amount of easy exercises.