Its defo a def, there is burnt tips.
But if it were a tox, a leaf that bad
Your whole plant would look like that.
So, idk what you given her
But looks to me like like you have a few issues
Sulphur, calmag and the really rusty spots on the outside is K. I also see you are suffering with curling leafs. Boost up the ventilation a little. Or drop heat by way of getting rid of some foliage
Good luck