So Question round 2:
Powersheilding lasers and their hitstun
Is it a different timing for high/low/medium lasers? I can always do medium and low but not high
Also, how many frames does it flinch you for before you can act again (both in air and on ground?)
It's a different timing yes. Because your PS hitbox is a circle around the middle of Sheik's body. Therefore, the timing closer to the middle of the circle going to be sooner because the circle sticks out more there, and for lower / higher it will be later.
16 if unstaled, 12 if staled.
How punishable is SH nair oos?
It can be very punishable. In my recent set with Mango I hit his shield with nair OOS and moved away from him as far as I could and he still managed to WD OOS shine me for it. I'm pretty sure some of the high level Foxes here have done that to me too.
I'm now vaguely interested to know if Sheik can grab herself if another Sheik nairs OOS on her shield. Off to the lab I guess...
I was thinking that Sheik could potentially have the same dash dancing effectiveness as Fox, Falcon, and Marth. However, I have heard two opinions that Sheik would prefer to avoid doing such since she has such strong options otherwise. Falcon/Marth sort of need to rely upon a DD method I believe since their normal attacks are pretty poor without it. Sheik on the other hand has very strong neutrals A attacks which would be preferred over the potential gain of trying to DD.
Her dash dance is incredibly effective for certain things but using dash dance as a primary strategy works better for those characters because their offensive tools are inherently more powerful (fast SHFFLs, stronger frame traps off said SHFFLs, Marth's d-tilt, a shine, Marth grab, gentleman, etc).
Sheik is more layered. You will not find much success with trying to overpower your opponent with speed like those three characters. You have to make the opponent afraid of your counterattack and then observe how they're playing around it (ex. if they're playing around f-tilt, they're gonna be dash dancing closer when you SH back but they'll maintain a certain space even after you land from the aerial). This maintenance of space & pre-meditated expectation of f-tilt is a commitment; both in terms of actions (they have to move & position themselves in this manner) and in terms of how much attention they can pay to something (human reaction time is faster when something expected happens & slower when something unexpected happens). So if you can figure out what they're playing against, you can create a lot of openings by simply not doing... whatever it is they're expecting / already playing around.
edit:
Running into dash cancel is amazing if you're really far. Walking is also very good with this character in general. Trots are also very good in general.