Lots of good info in here already, but in my experience, the MU can be summarized like this:
Anticipate needle camping and be patient. PS whatever you can, and try to steadily move toward her. Try to discourage her approaches with DTilts and jabs. Challenge her SH FAirs with SH BAir walls. Be prepared to fight back offstage against FAirs with UAirs or NAirs. I've noticed Sheiks like to use bouncing fish when you get too close, too, so once you start getting close, anticipate some aggressive manuevers on her part.
Some Sheiks will use use their jumps confuse you, scare you into your shield, and jump behind you or something. If the Sheik uses a FH or DJ in front of you, NAir them. If they try to go behind you, either run in the opposite direction, or try to NAir. FTilt can be punished on PS with jab, but if you just normal shield, just roll away. The important thing is to be ballsy in the right places. For instance, it's a better risk/reward ratio to just throw a NAir out if she's jumping all over your shield space, than it is to sit in your shield and wait for her to do your plumbing.
Most everything you do's gonna require hard reads though. There's really nothing in this match that Ganon has that can directly answer Sheik. More like just know what Sheiks typically like to do so you can think a few steps ahead. For example, intercepting a bouncing fish rather than trying to punish it, e.g. if a Sheik tries to bouncing fish you as you're waiting near the ledge, try your luck with an FSmash, the same you would against a Diddy who recklessly side-bs onto the stage. Or if she does it onstage, instead of trying to directly punish it, shield the BF and run towards her. This'll close the gap and force <some> kind of reaction, so reading that reaction is what I mean by thinking a few steps ahead.
And above everything: be patient. No matter how many needles she throws at you, you're one hit away from evening it up.
Here're a few sets against a Sheik that might have something useful in them: