Okay I have another theory for future appearances of Sird. Not saying it will happen (probably won't happen exactly as I predict) but I bet it'll follow a similar trend.
After Sird escaped from Riley as mentioned in the Platinum chapter, Mewtwo caught up with her in the Sinnoh region. Sird continued to run away and eventually she was forced to go to as far as the Unova region to shake him off. There, Sird found out about the affairs of Team Plasma and she discovered Ghetsis's plot to sabotage the Pokemon League. Wanting to find out more, she disguised herself as Hood Man and partook in it just to get close to Plasma's big attack. And then going into the events of Black & White 2, Sird finds about about some plot by Ghetsis to host a world tournament (yes, I'm also predicting with this theory that the PWT will be organized by Plasma). Interested by that and also figuring that it would be a good place to gather all past Dexholders so that Sird can snatch them all at once, Sird feigns loyalty to Ghetsis to get in on the plot. Oh and I'm gonna predict that Mewtwo will catch up with Sird in Unova eventually and soon encounter Genesect, a man-made Pokemon created by Plasma similarly to how Mewtwo was created by Rocket. Mewtwo fights Genesect like how it fought Deoxys, another Pokemon created in a similar fashion as Mewtwo, and it will get to showcase its signature move. Oh yes, and in the PWT, we will get to see Ghetsis unleash his plot as well as Sird doing her own thing. The Unova Dexholders will try to stop Ghetsis while the other Dexholders will finally get to finish off Sird since they all had some form of conflict with her, either directly or indirectly.
EDIT: Oh actually, scratch the line about Sird finding out about Ghetsis's plan to host the PWT. Rather, Sird manipulates Ghetsis to host the PWT, convincing him that it's a good idea for Plasma and Ghetsis's plot but in reality it's just a ploy to get all the Dexholders inside one stadium at once.
2nd Edit: Oh and if Sird really is Hood Man (okay I know I'm being really bold with this theory since it's not even confirmed yet who Hood Man is) then maybe she's wearing the armor for similar reasons with Guile? Maybe she was severely injured in the battle with either Riley or the chase with Mewtwo that she was forced to wear armor that preserves her body?