Food advice please!!

Hi everyone!! I’m new here :->
I’m looking for some advice for my dog, she’s a spayed 5 year old German shepherd, we’ve had her for about 6 months and when she came to us her food was Jameswellbeloved and butchers tins, her owners said she was a grazer feeder and would just leave a bowl of food down for her all day. Since she’s been with us we’ve switched her over to raw and she’s been on it with no issues for I think 5 months as we switched her just a bit after getting her. We use ProDog Raw but for the past 2 weeks we’ve noticed her itching a lot to the point she gets these red sores on her, I’m unsure if it’s the food or something else, it could be the chicken as I know lots of dogs usually have allergies to chicken, I don’t know if I should change her food or try and find a supplement for itchy skin to add to her food? Some advice please I’m a newbie to all this dog food info :( :( Oh and she’s also not a grazer anymore, she’s a piggie :)) We’ve got 3 other dogs so there’s no way we could’ve left a bowl of food for her all day without the others eating it all, she gets 2 meals a day and eats everything :)) :-