I am worried about my mother’s mental well-being while she is caring for my 85-year-old grandfather with dementia. How can I help?

First of all, be there for your mother. Most importantly that means just being available to listen (without interrupting or talking about what is affecting us). While I directly care for my in-laws, my own mother is in a similar situation. Usually, our moms are, well, moms. They don't want to worry us, or they try to 'protect' us from these situations. (Like that works!!) So, your mom may not come right out and say what she needs. However, if you are a perceptive listener, (1) that may be what she needs the most, (2) you may pick up on minor details that may help. For instance, is she tired, or just grabbing a quick snack? Maybe you could arrange for a respite visit with your grandfather to give your mom a break, or perhaps fixing a well-balanced meal that will also be an appetizing leftover? A key I have learned is that caregivers of AD patients need an extra amount of nurturing. They give so much, and yet don't get it in return. So be there for your mom! I know these things are minor, but you might be surprised at the results!