depluming mite & treating ?

my vets prescribe frontline spray for my birds but as this isn't licensed for poultry you should get it from a vet and sign for it 

Its not cheap though, I got some off my vet yesterday as a precaution so I don't need to race down if I ever need it.  He advised an egg withdrawal of 28 days so be aware of that. 

Hen with poorly neck has passed away today 
Had treated with purple srpay & diatomed dust bath area & coop and hens to make sure, she was lots better scraching around early thsi morning then this afternoon I looked out and she was fluffed up in the run - on investigating further found her to be hardly breathing 
I brought her in and checked her but her neck was very floppy she sat in my lap and passed.

I am so sad 

We only got these 4 pol bantams on 10th November, I had one die overnight within 2 weeks of getting them (she was the smallest), we went back to lady & she let us pick another f.o.c
This we manged to be accepted by the remaining 3 and all was good until my one Alys was poorly - vet was pretty certain it was Maereks disease ??  Now she seemed to think that if that was the case all of them would follow the same fate within 2 weeks of each other. Alys passed on 27th Jan and all other 3 seemed fine until the issue with this one.  Now I am unsure as to whether I am doing anything wrong or whether I have just had some bad luck 

So sorry Mega.   

I am just catching up on everyones news after being away for a week.  I hope that your remaining hens are well and you have better luck from now on.