This is a hard part of being a caregiver. Being criticized or otherwise subjected to cruelty is never pleasant, but it’s especially hard to take from someone you love and are trying to care for. The nicest people can act in ways that completely shock us when dementia is involved. They are experiencing a disease that makes them unsure of themselves and the world, so they are on edge. They are frustrated by their loss of autonomy.
The part of the brain that would normally make them think twice about what they say, or “bite their tongue”, no longer works. You, unfortunately, are not only a convenient target, but also a safe person for your mom to lash out at. The best way to protect your feelings is to put on some symbolic armor. Prepare yourself before your visit and practice your response. Perhaps when she makes a hurtful remark, you take a deep breath, and say “I’m sorry you’re feeling this way. I love you, and I’m doing my best to help.” Try a change of subject, or moving to a new activity to break the mood.
If you need to, walk away for a bit and come back. If those things don’t work, it’s okay to cut your visit short, tell her you have to leave and when you’ll be back. Remind yourself that you are doing a good job, and always remember to practice self-care so you are not caring for her at the expense of your own health.