A New York woman has pleaded guilty to a charge of second-degree murder in the stabbing death of her mother, according to the Franklin County District Attorney's office.Investigators say Alexa Gallagher, 26, of Tupper Lake, stabbed her mother with a knife in July 2022.Police found the body of Melissa Guisewhite, 51, in a home on Lakeview Avenue in Tupper Lake. Sentencing is scheduled for May.