What law do you break when you put a pain killer on doctor's prescription?

my sister is a pill addict she is having a problem with vicodin. she might have a problem with something else who knows she lie's alot anyway. she took one of her prescription's that she given to her for a ear infest-ion. my sister put vicodin on the same prescription and turned it in to get filled. now the cop are calling say there's been a complaint filed again her. i was wonder what law's were broken and how much time she may be looking at this is her first time for something like this but i do believe she been red flag before.. it a sad thing i just feel sorry for my nephew he's 2 and her and her husband (his dad) are both addicts. she told my mom yesterday that she was good mom.........