Hot spots are usually irritated skin + skin infection, often staph, but don't panic because I've never heard of anyone catching staph from their dog. I was a vet tech for four years and cleaned up hot-spots literally every day. They're extremely common in hot, humid climates.

Benadryl either helps the itchng or makes the dog too sleepy to scratch, depending on who you ask (slip a pill in a treat). Sometimes the vet will prescribe antibiotic pills and/or an antiseptic wash to help get the skin infection under control.

Luckily, since this is new to you, it sounds like your dog doesn't have a chronic problem with it. We see a lot of recurrent hot-spots related to pollen and flea allergies here in SE Texas, Allergen Capitol U.S.A. Sometimes the dog gets to itching and the more he scratches, the more irritated the skin gets until he has a disgusting little infection.

The skin mostly needs to be kept clean, dry, and air-circulated. Be sure the rest of the dog is clean and flea-free, although flea allergy hot-spots often occur on the butt instead of the neck so hopefully it's not that. If she's already not scratching it should clear up pretty fast.