How to brush a compromised elderly person's teeth?

My mother - 85, mostly bed bound after a stroke and repeated infections - eats a ton of sugar. She drinks Ensures every day, plus juice. Lately she is obsessed with chocolate. She has lost a ton of weight since her stroke two years ago, and has gone through long phases with no appetite, so if she wants peanut M&Ms all day, her 24/7 aides give them to her, with my approval. She also drinks veggie smoothies and now wants sandwiches and pizza as well, so she is getting other, better sources of nutrition. Today I asked her aide to make sure she brushes my mom's teeth. She said the "care plan" from the agency says to do it every 3 days. I was shocked. It hasn't even occurred to me that her teeth weren't being brushed daily. Aide (who is wonderful) says she gags/chokes. There must be a way to keep teeth healthy in an elderly person in my mother's situation, right? The last thing she needs is to lose her teeth. Eating and drinking are among her only pleasures.