"Who Threw the Overalls in Mrs. Murphy's Chowder?" was written about 1898 by George L. Giefer and recorded by Thomas Edison in 1901. As such, it would have been extremely contemporary music for Helen to be playing and stands in stark contrast to Tibby's classical taste.
Despite Tibby's prior reference to Beethoven (regarding composing/performing while deaf), the piece that Tibby plays around 23:30 after Margaret's exit is actually Chopin's Nocturne No. 15 in F minor.