My input matters a lot less, rpg, but I have a little bit of a problem with your second semblance idea: Since it involves consciousness-shifting from one version of events to another, it sort of assumes that Amber is always in "focus" and our characters are simply the (minorly) alternate reality versions of them, otherwise either Amber would basically have disappeared or nothing would have happened, from our perspectives.
...and for a much simpler reason: even minor, IC retcons can get real messy.
Oh, don't get me wrong, it would be difficult. The second one is mostly supposed to be enemies, but could also just work for if someone wanted to change their action basically, or effectively to allow retcons with an IC reason for it. It's less that Amber's in focus(at least to me view of it, since it's not exactly the easiest thing to describe), and more like she's shifting the other reality into this one. Sometimes, other people can notice how everything changed, but most people just shrug it off as Deja Vu or mental vertigo or the like.
The first one involves seeing a short ways into the future, and seeing Truth, which can also be awkward.
I don't really mind either way, though. The first one would probably be easier over all, and make it so Amber was less of a 'look at me and my even special-er snowflake character'.
Also, Amber's backstory is basically that she's from a really rich family(stupendously so, not just mildly rich; like, Oil Tycoon Monopoly levels of rich), but they didn't get there by being nice, and they're worried Amber doesn't have the right stuff to keep up the family fortune. So, Hunter/ress School.
Also she's really good with her weapon and it's really high quality. Which is why the whole 50 Weapon Skill thing.