I agree with Taz, momcat, and Catmandu. Maybe a kitten would be a bit of a bad idea, but a calmer, more reserved adult might do wonders. But for now just give her your undivided attention until you decide, since she needs all the comfort she can get!

I'm so sorry for your loss, kidney failure is a horrible thing. That's how my dad's dog, Comet, died. I know how much it can hurt, and it must have been just horrible for lovely sad Penny. I hope things work out.