Just an FYI: Not universally true. I managed to teach full-time (quite effectively) while severely depressed to the point of requiring hospitalization multiple times over a period of years. I was always very high functioning on the outside - a mess on the inside. I'd reach a point where I needed hospitalization, but even that was usually just a few days until stabilized and then straight back to work. Some people like myself have this odd ability to compartmentalize. It's why I could still function and teach very effectively while my husband was in the ICU and dying, and I've been able to do so since his death. It doesn't mean my grief is not severe or that I don't collapse in mental exhaustion once home. I've known a number of people who are high functioning even when really struggling - it's a paradox, but not all that uncommon.

In this particular case, it sounds like her mom has offered to help her with meals out of the kindness of her heart, and she took her up on it. Doesn't sound like she's depressed or lazy or helpless - just utilizing an offered resource available to her (delegating which is a characteristic of many effective leaders and business people). OP, I would just be clear if I was moving in with her that you are each responsible for your own groceries, meals, cleaning, etc.