Has she been diagnosed with arthritis or do you just suspect that she has it?
My old cat, George, needed help to get up on the bed and I built a little step for him to use. He still preferred leaping onto the bed, missing and landing on a heap on the floor screaming in rage. When he did get around to using the step it was much less troublesome for him.
Have a read of this and see if it helps you in any way
http://www.fabcats.org/owners/arthritis/info.html
How old is the young lady concerned?