Mother needs to gain back 20 + pounds after polymyositis flare up

I am writing for my mother who was working full-time as a teacher at 85 years old before a severe flare up in November. She has had polymyositis x 15 years. Her doctor at the time did not recognize she was in a flare up, so it went undiagnosed until the end of January 2026 when she saw the new rheumatologist. Also now diagnosed with dermatomyositis that she has probably had x 5 years. She has had to retire and is unable to walk more than 150 feet due to significant loss of weight and muscle mass. She is on CellCept and Immuglobin IV treatment monthly x 2 days. She could not afford to lose 30 pounds and now weights about 70 pounds. Any suggestions for weight gainer supplements for her to take that are unflavored and not gritty that can be added to milkshakes, gravy, mashed potatoes, etc without her noticing?? She also consumes Boost and Ensure. She has difficulty swallowing so she really is unable to eat enough food to gain her weight back.

Thank you in advance for any suggestions.