She looks much much older. The face is chubby and her eyes are very puffy and swelled looking. Misty's not that big of a chicken. The posts of her taunting Amber then getting into a fight over Ron along with the quick 911 calls and telling off the driver for taking her to that neighborhood prove it.
Misty also demonstrated symptoms of a "flat affect" during her court appearance which makes her appear older. A "flat affect" means "a severe reduction in emotional expressiveness. People with depression and schizophrenia often show flat affect. A person with schizophrenia may not show the signs of normal emotion, perhaps may speak in a monotonous voice, have diminished facial expressions, and appear extremely apathetic. Also known as blunted affect."
http://medical-dictionary.thefreedictionary.com/flat+affect