This is salt build up and if you are seeing that in the drain pan then it is in the soil as well and by the sounds of the leaf you are talking about its at a toxic level. You need to flush with clean water as son as you can, i am assuming that you are in soil, so you need to push out more than the actual size of the container. So if it is a 2 or 3 gal you need to flush with at least 3-4 gal of water.
How far along is she, if i had to guess id say you are somewhere in flower at this point? If you are the salts are from the ferts that you have been using over time. have you supplemented clear water between feedings? did you give her a flush at any point during the grow?
EDIT: Moved Infirmary due to plant health issues