What can be done about Mom's failure to thrive?

You need to have a face to face meeting with her care team to see what they recommend and are willing to do for her, it sounds to me like her care needs are greater than an AL will handle and it may be time for a nursing home. In the meantime provide plenty of high calorie and high value snacks and supplements like boost or ensure.

There's another product that my father has found more appealing than basic Ensure. It's Ensure Plus, and was served in the hospital.

helpmom, there are many reasons an elder doesn't want to eat.... they lose their taste buds so everything taste blah, except for sweets [my folks ate a lot of sugary foods].... another reason could be that their teeth hurt but they can't communicate that to you.... another reason is an appetite because they aren't burning up calories to begin with... some prescription medicines can have a side effect of no appetite..... with some their stomach hurts too much due to the organs are starting to shut down [sad I know].

For my Dad he wanted to eat but he was aspirating his food, thus it was going into his lungs. Sadly there wasn't anything anyone could do as putting in a food tube was something Dad didn't want.