My beautiful 22 month old Crossbreed 3/4 Staffordshire bull terrier 1/4 English bull dog , last week out of no where come out with hives . Took her to vet , got a steroid injection and pendicare for three day , great.. but they have come back not as bad but still a few .. .. we think it’s due to plants English Ivy , .. any advice as I’ve never had a dog wiith allergies before.