Welcome back to the forums. 
It's important that you carefully observe how your budgies interact in order to then make a decision. If your male is truly trying to pluck and even sucessfully plucks any feathers off your Darwing, then this calls for immediate separation because that is aggression.
If you have to house your budgies separately, in time they will both adjust to the change. You can help them out by giving them extra support during that time.
The fact that the flight feathers aren't coming back is also a matter of concern and given your Darwin's current feather condition, it would be best to have her examined by an avian vet specialist and tested to see if she is a French moult carrier.
About the grit, it's simply best to replace it for a cuttlebone/calcium block and a mineral block.
You can check this link for the detailed info: http://talkbudgies.com/articles-diet-nutrition/103925-truth-about-grit.html
It's important that you carefully observe how your budgies interact in order to then make a decision. If your male is truly trying to pluck and even sucessfully plucks any feathers off your Darwing, then this calls for immediate separation because that is aggression.
If you have to house your budgies separately, in time they will both adjust to the change. You can help them out by giving them extra support during that time.
The fact that the flight feathers aren't coming back is also a matter of concern and given your Darwin's current feather condition, it would be best to have her examined by an avian vet specialist and tested to see if she is a French moult carrier.
About the grit, it's simply best to replace it for a cuttlebone/calcium block and a mineral block.
You can check this link for the detailed info: http://talkbudgies.com/articles-diet-nutrition/103925-truth-about-grit.html