The pedigree could be tough. Unless you have a bill of sale or something giving her registered name, you may never be able to get an official one. If you just want to learn her background, you might luck in and find a local breeder that remembers selling her to the original owner. You can find breeders in your area at
American Kennel Club - akc.org There should be more info on pedigrees there too. Most breeders will know more about pedigrees than I do.
Pull back the hair at the base of the tail. If you see, or feel dark, reddish specks, she doses have fleas even if you haven't seen any and should respond to flea remedies. You may also need to treat the house and yard to be free of them.
For itching, feed a decent chow and little else, brush regularly, and bathe seldom if ever. If after a month of that, she still itches, talk to the vet.
For temporary relief you could try some Benidryl, up to 2 mg per pound of body weight. Such self medicating needs to be limited.