I can't remember exactly what it was, but there was something in the ECHOs near the end of the game, the ones where Angel is a kid, that made me think that Jack somehow TURNED Angel INTO a siren when she was a kid.
The story has never intrigued me much so i haven't given it much thought, but the whole "Siren power is given or taken" thing would make much more sense to me than being born with it given that there supposedly can only be six in the universe at once. That to me, says that there are only so many sources of the power, not that they somehow get reincarnated with it.
If this were the case, and let me remind you there can always be retcons, then they could do a lot more with the Siren story line than otherwise.
Imagine if in BL3 you play as Sirens, only you know, ninja siren, turret siren, etc. I would definitely welcome a super power on top of special power. Why not? Maybe Siren powers could be a passive that you choose? Dunno, but it would be cool IMO.
http://www.youtube.com/watch?v=GtxCr5ju2EE&feature=related - If you played Mystical Ninja 64, you need to click this.
Steele was painted up because she was one of the girls that jacks people painted and brought to him. Which is why he sent out the echo telling them to stop painting girls and trying to pass them off as sirens.