1. Starfleet has used Lore's, or B4's body to build an army of androids and I'm guessing Picard's relationship with Data, then B4, put him at odds with Starfleet about this, maybe this is why he resigned, his beef with Starfleet if you will.
The Androids being sentient, may have revolted and attacked the federation because they realized they were being used as war fodder and wanted to be free, or at least enjoy the rights Data had, again, I'm guessing Picard may have had a problem with creating androids to be exploited by Starfleet, this could be the moral split with Picard and Starfleet.
Picard must be troubled with Data's legacy being exploited in such a heinous way.
2. The Romulans, or a faction within what's left of the Romulans, either see the Federation developing an army of Data-ish androids as a threat or maybe they just want to gain an edge after losing Romulus and have decided to exploit Borg tech to make themselves some sort of super soldiers.
Maybe that's why Starfleet developed the Androids, in response to the Romulans playin around with Borg tech.
My guess is, 7 of 9 gets into this because of the Romulan's meddling with the Borg tech, perhaps she's trying to stop the exploitation of whom'ever is being assimilated against their will, or perhaps she just has a beef with the Romulans playing around with Borg tech.
The girl, I'm guessing she has a connection with the borg, it's been stated that she may be a borg queen and maybe the Romulans had that in mind, a borg queen they, (the Romulans) could control maybe a queen would be necessary to control these super borg soldiers, and maybe she escapes from the Romulans and is on the run from them, seeking out Picard because of his history with the Romulans, or the Borg...
They could have created this girl using something from the ship that either had queen DNA, or some tech that would/could transform her to one they could then use.
She also could be a recreation of Data's daughter too. But I'm guessing she more likely has the Borg connection instead.
Picard - may be also starting to see signs of that syndrome and may see this as his last chance to make a difference, set things right before his condition becomes more advanced.
I can't wait to see how this plays out.