Okay, yes, yes, ever since the New 52 we've had to deal with the fact that characters are a little different. "Not the way we left them."
However, I think Harley Quinn fans may have a bit more on their side. "She's not the same!" we cry out. "No, it's a reboot, she's different!" you retort.
I have reason to believe that she is actually a DIFFERENT PERSON.
Mild spoilers if you haven't read Suicide Squad #15 :
Here, Joker states that there have been many Harleys before this one. He has a constant influx of them. This Harley being a literal different person, and the "old" one being dead or gone, explains the radically different attitude, outfit, and backstory. Also the fact that so far, Harley has shown no actual history with anyone besides Joker -- she has yet to even mention Ivy.
This Harley was unable to snap out of those manacles like they were cardboard, and was also poisoned, which means that she doesn't have powers and never took Ivy's potion.
Think about it.
Edit: If it actually plays out like this, I get boss level bragging rights until forever.