The incident happened at the Wisewood Inn, a Loxley Brewery pub in the picturesque Loxley Valley which has won CAMRA awards.
South Yorkshire Police said: "It is reported that on 12 February at around 7:45pm, the victim was sat inside the Wisewood Inn when her dog was attacked by another dog. When she attempted to separate the animals, she was bitten on the hand.
"Her dog suffered injuries that required treatment from a vet, and she has suffered nerve damage to her finger.
"Police now want to speak to anyone who witnessed the incident, or anyone who can provide information about what happened.
"If you can help, please call 101 quoting incident number 612 of 12 February."