You know what the answer is. Only a veterinarian that has examined your dog can advise you.
I would refrain from trying over the counter meds and home remedies. Sun block is not intended for veterinary use. You could be making the condition worse.
The sooner you get her to a vet and properly diagnosed you will know what you are dealing with and what the treatment options are.
PS: They have 24/7 emergency/walk in veterinary clinics all over the country. They will communicate with your vet via phone/fax as deemed necessary.
She may need medication, such as steroids to temporarily stop the suffering (pruritus) and risk of skin infection. You may be referred to a specialist for further testing.
14 hours, 6 minutes ago
