need a bit of advice on my border x patterdale bitch, she is 3 in july, she has always had a bad coat i've tried a few things to try and improve it but just no good, its always been very shabby and different lengths, i take her out for a little bit of bushing and her face and back, end up nearly bald then i have to rest her up for it to grow back, i've 2 other terriers they do all the same work but they never end up like it. any ideas as its doing my head in