it means the character is a wish fulfillment device for the author

needed to clear this up b/c apparently some people on the web are calling mandy a mary sue now

it can mean either

maybe you could argue that the word has changed, but historically that term is associated strongly with author avatars

but no mandy isn't a mary sue in any way, but she IS kinda boring

lol what

mandy is hilarious and awesome, she makes the show

"Mary Sue" doesn't mean the character has no flaws

https://en.wikipedia.org/wiki/Mary_Sue

A Mary Sue is an idealized and seemingly perfect fictional character, a young or low-rank person who saves the day through unrealistic abilities. Often this character is recognized as an author insert or wish-fulfillment.

It's both.