Why do those with dementia get so mean?

My MIL, who has rapidly advancing dementia (moderate-moderate severe), has gotten very nasty with us recently. Every morning (and through out the night) she’ll start throwing clothes we’ve folded down the stairs and accuse of things. She’s accused us of stealing from her, trying to put her in dirty clothes, saying we’re mean, has called us a variety of cuss words, says I don’t know how to keep a house and a social worker is going to come take my child because I don’t know how to keep a house (the house is spotless). She told my husband that we’re only “here for the money” and some other extremely cruel things. She wakes us up at all hour of the night to accuse us of things as well. We’ve done nothing but help her - she lives with us, we do her laundry, cook, administer her medications, take her places when feasible. We’ve accommodated her needs in our home as much as possible. She doesn’t have the right insurance to pay for a nursing home and she has some money but not enough to cover all expenses. I’m at a loss here. How can someone be so cruel? We are at our wits end and could use any advice or encouragement.