Hello and thank you for using this site to help you. If the belly area is itchy and she is licking or chewing the legs then you may be looking at allergies. It can be allergies to food or airborne allergies.
Sometimes changing the dog food to one that is made specifically for allergies can help.
If it is airborne, it has been a very tough year for allergies in dogs. Benadryl can help and is given at a 1 to 2mg per pound of body weight.
You may also want to get a skin scraping done to make sure you are not dealing with something bacterial, fungal ,yeast or mites.
here you can read more on allergies in dogs http://www.veterinarypartner.com/Content.plx?A=597
Benadryl is given every 12 hours. There is also a new product for allergies called apoquel that you can talk to your vet about.
Something that may help with the skin is coconut oil. I will put a link below so you can see the benefits