Annie Oakley, being an historical personage, is in the public domain.
Dell Comics paid a licensing fee to the company that produced the TV show starring Gail Davis. Clearly, Dell felt that Davis' likeness was a bankable asset and added Annie Oakley to their stable of licensed Western properties.
Charlton comics, on the other hand were notoriously thrifty. Charlton simply created a Western comic with a female lead, named her Annie Oakley and presto! They were in the Annie Oakley business. Charlton's Annie sports a pony tail and blue jeans.
From Gunfighters #56- October, 1979.
The historical Annie Oakley (born Phoebe Ann Mosey) was a very petite woman from the Cincinnati area. None of the pictures I've seen of her show her in trousers.