Liza Weil is in fact, portraying Carole Kaye who is 84 years old today-- one of the most prolific recorded bass guitarists in rock and pop music, She played on an estimated 10,000 recordings in a career spanning over 50 years. She also particularly liked to use the upper register on her electric bass, while a stand-up double bass would be used to cover the low end. (accurately portrayed in the episode)
Liza Weil is a member of the Sherman-Palladino universe: she played Paris Geller on The Gilmore Girls. (It is a small universe: her ex-husband, Paul Adelstein, appears in the episode before this!)