When are "and" and commas used in a list of adjectives? For example,
- Poor little rich girl, or
- Poor, little and rich girl (or Poor, little, and rich girl)?
As was stated in a comment, this is a poor example for punctuation usage. The familiar term "poor little rich girl" is oxymoronic, in that "poor" and "rich" have opposite meanings. Perhaps she's poor in spirit, because her wealth has made her lonely. It's a tongue-in-cheek expression.
The Poor Little Rich Girl was a play that was written in 1913; it has been adapted for film at least three times, once as a Shirley Temple film in 1936.
If you really want to address comma usage, we should change the example. A general comma rule is, "Use commas to separate three or more words, phrases, or clauses written in a series."
So, we might say:
Following the comma usage rule, commas are used to separate the list of adjectives that describe Helga, Linda, and Jessica.
But the more familiar "poor little rich girl" could be used a standalone saying, where the commas would be omitted:
Danielle: I just got this manicure yesterday, and I've already chipped a nail!
Dan: Oh, you poor little rich girl!
Poor little rich girl is definitely one girl, one person, while poor, little and rich girl may be 3 persons, but also may be only one. This is therefore ambiguous.
As for the comma before and that's called a serial comma and Wikipedia has an amazing article explaining everything you need to know about it.