My husband is in mid-stage Alzheimer's and still quite functional for many things - his own grooming, helping with housework and yardwork, caring for our cat's feeding and litter box, and so on. However, he has a lot of trouble expressing himself. He starts a sentence, loses the next word he wants, and in the process, forgets his thought entirely. His input is good - he understands what I'm saying. His output is bad - he rarely finishes what he starts to say, and I'm left asking if it was about this or that so he can answer yes or no.
So if my husband is losing speech in mid-stage, and your mother is at the stage of requiring feeding and bathing by someone else, I'm not surprised she is losing her ability to speak. You have my sympathy with how hard this is, especially as is sounds like it could be the last stage. Remember you're not alone in this, and use this site to vent, question, and grieve, but also to celebrate any small thing that gives you a smile.
Despite his loss of conversation, my husband still gives me the warmest hugs, we still enjoy walks at sunset and ice cream cones and funny movies... There are still moments of joy in even the darkest times. Hold on to them. Keep a daily log of them if it helps: for instance, "Today Mom laughed at my joke and sounded just like she did when I was little."
I wish you and your mom strength and peace and moments of joy.