Elizabeth Mary Coster (born 11 December 1982) is a New Zealand former swimmer, who specialises in backstroke and butterfly events.

Swimming in heat two, she edged out Singapore's Joscelin Yeo to take a third spot by two-tenths of a second (0.20), but shared a twenty-third place tie with Sweden's Johanna Sjöberg in 1:00.61.

[3][4] Coster also teamed up with Hannah McLean, Alison Fitch, and Annabelle Carey in the 4 × 100 m medley relay.

She swam a butterfly leg in heat one with a split of 1:00.38, but the New Zealand team settled for sixth place and thirteenth overall in a final time of 4:10.37.

[9][10] Followed by the next morning's session, Coster fell short in her bid for the final, as she finished her semifinal run with a slowest time of 1:01.45.