Fon ear scab + vet visit

Fon has been scratching her left ear for 3 days and there is a little crust on it. I thought it was just dirty but no, the vet in Pinklao said it looks like allergy, maybe from the new dry food I bought. Got a cream and some tablets for 5 days. The vet also checked the ticks because we live near the canal and Kitkat goes outside sometimes. Kitkat is fine, no ticks, she just looked at me like I am crazy for putting her on the scale. I feel bad because Fon is only 1 year and 8 months and this is her first real health problem. Her skin is still ok and the ear is getting better already. Diet change slowly now, the vet said do it over 1 week not all at once.