Is she getting bitten by flies while she is out there. That can cause rough patches on the ear tips. They sell something called SWAT at TSC. It repels flies and smears onto the ears ever few days when the flies are bad. Flies can be horrendous in wooded areas. The clear is best. It dries and your dog's ears aren't all pink.
Not sure if that is what it is, but it could be.
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