This is how I see the sheik MU:
if she is at low %, you have 2 setups into death (dair->grab, and grab)
when you are at low %, CC her dash attack = death for her
jab her grab, if she shields at least you can roll away without being grabbed (maybe not if they are perfect, but in my experience)
If you can get her to shield a lot (usually what people do vs ganon), then it's time to catch them off guard with a grab.
Edgeguarding is actually easy vs her, unlike some chars
And she'll kill you off grab at any % (or should). Teching her fairs into the ground at high % is very useful, and so is teching the stage upon recovery (so she should basically always kill you from offstage). DI bair and fair perpendicular; it's very hard because the low angle of knockback for both but every attempt at coming back is a chance to change the entire match. Watch out for dsmash at the ledge because if you walljumptech it, it will just hit you again and probably kill you. I think that if you just walltech it, fall a little bit then upB, you might be able to avoid the other hits (but it's probably too slow to grab her while she's in lag). I will have to experiment with this.
In that MU basically 1 punish = 1 stock for both players, so play careful and choose your openings wisely, then once they are nervous ("I can't be losing to a Ganondorf!") you punish their ****ty mistakes