I saw that episode, and remember on arrow Nyssa told sara that Ras hasn't released a member from the league in years? ironically​ the member he released decades prior was Sara herself (who had gone back in time) I like how they brought that full circle.

The show made sure to imply that Nyssa was not the only Daughter of Ras. The league members always referred to Nyssa as "*A* daughter of Ras Al Ghul"
"A" not "THE"