The gym is my sanity. Without it, I feel like a different person. I feel lost and disturbed and mentally unsteady. Cardiovascular exercise makes me feel like everything can be okay. No matter what happens, no matter how "bad" she is, the gym can make it better.
The gym burns calories. And when she burns calories, she doesn't think how great that could have been for her heart. No. She very specifically and simply thinks, 'hmmm, well if this elliptical machine says I burnt 350 calories, that means I burnt off the peanut butter I slathered on that healthy english muffin I had this morning and the blue cheese crumbles I had on my loaded-with-veggie salad for lunch.' So, now, it feels okay to her to have eaten it.
If she burns off the "bad", life can move on. Sanity can stay put, and all is well in the world once again.