The 30-year-old alleged victim said her mother-in-law, 44, whose name was not released, was arguing with her husband while they were all drinking at about 3 a.m. Sunday at a Las Cruces apartment, the Las Cruces Sun-News reported Thursday.
The woman told police she tried to intervene in the argument because it was becoming "very intense."
The mother-in-law allegedly "grabbed (the victim's) right breast and began to squeeze and pull on her nipple" during the argument and refused to let go until the younger woman punched her in the face.
The victim said she kicked the older woman out of the house and soon discovered fluid in her breast and her nipple fell to the ground when she lifted her shirt.
Police said the victim, whose nipple was reattached Sunday at Memorial Medical Center, told officers she did not want to press charges but prosecutors are weighing a possible count of felony aggravated battery against a household member.