I wouldn't, and I don't rehome kittens where there are senior cats, I have senior cats and foster cats of all ages, and mine have never tolerated anything under the age of 2, as the youngsters just want to play and dive on them, and not only do mine not want that, but i think it is unfair to put them through it, they deserve some peace in their senior years - if you switch it into human terms, it is like a grandparent constantly having to look after a grandchild. However lively her 20yo is, I think it would struggle with a single kitten wanting to play constantly. I can understand a cat pining, but I think she would be better off with an adult.