Worst case scenario? Under the 2005 Identity Theft Penalty Enhancement Act, she could get two years in prison.
In reality? She would probably not be charged with identify theft, but rather use of a false ID. Use of a false ID is a misdemeanor in New York, punishable by up to one year in jail and a $1,000 fine. Specifically for using it to misrepresent one's age or that of anyone else under 21, the penalty is a $200 fine and/or up to five days in jail.