Sassafras is a slang when someone is called "sassafras" it means the person is rude, sassy, impudent or disrespectful. Source: http://www.urbandictionary.com/define.php?term=sassafras

As I think you know, sassafras is the name of a plant, from which tea can be made. Perhaps the person nicknamed "Sassafras" liked to drink this tea. There are some towns named Sassafras, too, in the USA, Australia and possibly elsewhere. Perhaps the woman came from a place called Sassafras. These are just wild guesses. We'd need more information to make a more educated guess.

It’s a southern thing. It means you are being sassy and kind of full of yourself. It is based on the plant. The sassafras plant and the tea made out of it has a kick to it that can make some people feel high. Basically you’re acting a fool like you’re high on sassafras. It’s a tongue in cheek way to call someone out and tell them to take a step back without being rude.