My former manager is trash-talking me to potential hiring managers, what should I do?

Call whatever manager is higher up than her, but does NOT work in the same restaurant. Make sure to sound professional when you relay the situation to that manager. Don't let dissolve into an even worse situation. Just say, "This is what she's doing. You can check my employment records to see that the information she's giving out is false." Let the manager decide how to proceed from there. I guarantee the "vindictive b*tch" will never answer a call about you again.