She a cutie! There are a lot of reasons for this. Most vets like to diagnose food allergies first.
I have found that dog foods all have something wrong with them. And it could be a intestinal nightmare for you and your girl if you get the wrong food.
Last summer, we found that most dog foods come from the same source. Sadly, there was poor quality beef that couldn't be used for humans, so it was put into dog food. This caused several families to lose their pets. So, switching foods may not help as there is very little regulation of pet food. It doesn't always contain the ingredients you read on the label.
She may have some form of contact dermatitis. In which case, you would notice her scratching.
If contact dermatitis is ruled out. I would use a brush with soft, highly dense brissels. Followed with a baby-wipe of damp shammy to pick up any loose hairs.
Often dogs will lose hair if they are nervous or scared. For example if you live near a busy street and she is disturbed by the noise. Or if you are gone for a while she may get separation anxiety from missing you.
I would get her a visit with her vet to check for other reasons. We have had a lot of changes in our climate and many storms, bring us new species of outdoor pests and such. She could be affected by this.
Good luck,
Teriqua