Just human

"no you don't understand Yn your just a stupid human"

"I know but I have to save him"

Yn is graces eldest daughter but Yn was born a human. grace had Yn merely a few days before she died. but then graces na'vi body gave birth to Kiri. Yn is younger then neteyam (I know time ain't adding up but that's how it's going) she is only younger by a month.
Yn was born with a birth defect meaning she couldn't go outside much. her body goes entirely numb sometimes.sometimes she seizes, but worst of all she get pains shooting through her body usually causing her to seize leaving nose bleed and her sometimes. coughing up blood. so she's usually in one of the na'vi machines so she can run with the sully kids and all of that since she can't go outside.