BW isn't over yet and B2W2 has barely even started. She probably won't appear in BW but I bet you that she will have at least a cameo in B2W2 because we know that Mewtwo will make some kind of appearance (due to its signature move) as well as the PWT where all the Dexholders will most likely gather. I know for sure that she will appear by the end of XY, though, because she is very affiliated with Mewtwo and we saw Mewtwo's new form. Maybe in the manga, Sird is responsible for Mewtwo's new form?
And we already know her purpose: to collect space-related Pokemon for her boss Cyrus while also spreading some evil around while she's at it. But since Galactic is dead, who knows what her purpose now is. Maybe she would have gone with the other commanders at the end of the Platinum chapter but due to Mewtwo constantly being on her tail, she was unable to catch up with her affiliates.
Image removed for making the signature too tall, too wide and over the 150,000 pixel limit.