The most common cause of what you are seeing is allergies or an allergic reaction.
There are some simple things you can do if your dog might be suffering from allergies.
I would talk with the vet about a different low allergy diet, one that will have the least reaction. Rabbit and potato is good, but you can choose another brand. Try steering clear of brands that have corn.
You should also get her on a flea preventative if she is not already. Even if you don't see fleas, it only takes one to get the cycle started.
I would also use a prescribed dose of benadryl, especially during allergy season. My vet recommends 1 mg per lb of body weight given every 8-12 hours.
Keep in mind that dogs can have allergies to pollen, dust and other household allergens so you should evaluate your home and try to make it as allergy free as you possibly can for her.
It sounds like the dog might also have a secondary bacterial or fungal infection. This is usually secondary to allergies and itching. This means that the secondary problem is caused by the primary.
When dogs scratch, they abrade the skin and allow bacterial and funguses to enter the skin. The result is a bacterial or fungal infection. This is what causes the smell.
You need to see the vet so that they can get a culture and tell you what kind of treatment is necessary.
While you are there, you should also speak with the vet about a supplement that has omega three fatty acids. Good skin starts from the inside out and this can be very beneficial.
Let me know if you still have specific questions about this.