how old is battery? It may be breaking down inside!!!
clean battery as said in other post.
i use the red/green felt washers under the battery connectors. then keep each post coated in heavy grease, but if battery is starting to break down inside, the white powder will continue to built.
I think battery is leaking acid fumes.
If it was my daughters car, i would buy her a new battery and retire that old battery to the old tractor or boat trolling motor.
good luck and be careful, that stuff will get all over the car fender, you, clothes, etc: