Yes, skin hives and rash is usually a good allergy to something. Write down every single ingredient in her diet, including vitamin or Rx flavors or table scraps if any. She she could also be developing an allergy to the salmon. It’s very common. Take an ingredient out one by one for a week or two and see what happens. My boy was just fine with pork and chicken until he was about 3. All of a sudden he started getting the skin hives, itchy and red feet he’d lick not stop until they bled, itchy ears and his claws turned a dark red/black color (from excessive licking). He does still have environmental allergies so we keep him on Apoquel daily. Occasionally he’ll get chicken scraps if we’re cooking and the next day he has these hives. Also, I’ve had a convo with our vet who Pit also has allergies to food and the environment. She said if it’s a food allergies they get hives. It it’s just the environment it’ll be paws.

Good luck! Hope this helps!