Bert the cockerel bully

Hi newbie cluckylil here, can anyone help with Bert?, he's a beautiful lad but very full of himself, he attacks little black hen (a daughter of his) only in the Summer, I have 9 hens
four are Bert's favourites, he tolerates the others, apart from this little black one.
I must admit she can be a bit of a baggage too, wonder if he knows she is a bit not all there??? in 10 years of having my fluffy clucks have not seen this behavior.   

Hi, Little Black Hen is about three years old and she lays eggs, so that rules that one out
 
I was wondering if there was a spray to put on her, or may-be a coat?
she has made friends with nextdoors cat, weird I know....
 

No, he's nasty, she has no feathers on her back now, she is very passive when he strikes,
sometimes hunching down when she sees him coming.

I echo Joyfull's comments and say get rid of the cockerel. It's not fair to the little one to have her permanently in fear of him.
If getting rid of him isn't an option, then see if you can rehome her, but the person taking her on would need to know she's had a rough time of it in order to keep an extra eye out for her.

Poor little thing!