Olenna Tyrell also teamed up with Ellaria, Daenerys, and Varys.
The sails of Highgarden (House Tyrell's castle) were also seen among Daenerys' fleet on the finale, which means Olenna has turned over all of House Tyrell's remaining resources to help the Mother of Dragons.
Olenna is seeking vengeance against Cersei Lannister now that her entire family was murdered.