By Rachelkat:

Grizabella is this really old cat who was really famous and 
glamourous when she was younger but now she's made bitter by 
Bombalurina and Demter and all the other young queens who sort of 
remind her of herself when she was younger. She comes back several 
times to see whether everyone will accept her even though she's most 
un-Jellicle-ish, being so old and sort of limping. Naturally, they 
don't. There are a few who feel sort of sorry for her, but they are 
stopped from touching her by the other cats.

I think Old Deuteronomy is possibly her father, because the coloring 
is similar and he feels bad for her after hearing her sing memory. 
She could also be the mother of Mr. Mistoffelees, because of the 
glittery stuff. Bustopher Jones is either Mistoffelees' father or 
Grizabella's brother, Misto's uncie.

Grizabella's past was good for a while, then she maybe got depressed 
because she wasn't beautiful anymore, or she left the Jellicles and 
then wanted to come back again, and that's why they won't accept her 
back.

I'm sort of glad Grizabella gets chosen, for one thing, she's really 
old already and she deserves a shot at another life, and for another 
she can leave everyone alone and quit whining about no one accepting 
her. I felt bad the first few times, but now it's just like, move on, 
Griz! You can still be happy.