We had the same happen with our youngest DC DD8,she's the only one of our 5DC that had cradle cap past being a baby and she had the worst cradle cap I'd ever seen,it was bloody horrible.
We tried the shampoo but it did nothing so we tried olive oil and it worked,it took a few weeks but it did work and really well.
Our DD was losing hair as well with the cradle cap,once the cradle cap was gone she did stop loosing hair.
She's 8 now and has lovely thick naturally wavy hair that's almost to the middle of her back,everyone comments on her hair. 
Like others have suggested start getting her to use softer hair ties for her hair and treat the cradle cap.
We put the oil on our DD's hair every night,I'd put it on leave it for about 30 minutes the first week we started doing it and then I'd gently massage her head and then rinse of with mild shampoo.
The second week we'd leave it on for 10 minutes then massage her scalp and then rinse it of with the shampoo.
You should find once the cradle caps gone that she stops losing lots of hair and it should start growing better.