from wikipedia..
Is Jodie too OLD?
Nancy was corrupted at the age of six by Fagin, the lovable but villainous person who persuades downtrodden youths to do his bidding. Her exact age is not mentioned in the book , although she has evidently been a prostitute for 12 years, and is visibly in her twenties or thirties in film versions of the novel.
Is Jodie Too FAT?
She is described thus when she first appears "a couple of young ladies called to see the young gentlemen; one of whom was named Bet, and the other Nancy. They wore a good deal of hair, not very neatly turned up behind, and were rather untidy about the shoes and stockings. They were not exactly pretty, perhaps; but they had a great deal of color in their faces, and looked quite stout and hearty."
So that's no and no.
Nancy is supposed to be "quite stout and in her late twenties"
The only think Jodie has "done wrong" is fallen foul of a couple of body facists on this show...