Sounds like numerous things - its possible - depending on her age -
the legs were due to arthritis or bone deterioration. Her lack of
appetite could be that or that her teeth were giving her problems. I
know several times that one of my parents cats would go on and off
with eating because she kept having teeth issues. This led to them
pulling about three of them that had abscessed and then regular annual
cleanings after that for all of my parents cats.
Really, without more indepth analysis, her waning strength and
appetite could have been numerous things.