My Mom has grown weaker and also heavier. Her aides and I are having difficulty moving her upwards in her adjustable bed. Any advice?

When my Mom was stronger and lighter, we were able to pull on her bed pad and move her higher in her bed. Now, when I come to visit, I often find her in the middle of the bed lying flat on her back even though she is fully awake. I feel this position is very bad for her state of mind. When I go to readjust her position, I cannot budge her -- she's just gained too much weight. I am trying to avoid getting a mechanical lift because I think that kind of machinery will depress her. I have two aides who have no trouble moving her up higher on the bed, but they are very strong women. Must I let go my aides who are not as strong and are now having difficulty, or is there some technique to readjust her more easily? When two of us pull on either side of her bed pad, we are successful, but I cannot afford to have two aides present at all times. Any advice would be appreciated! Thank you!