Sheik can CC Fox's Nair to Dsmash or a tilt. This ***** Fox's staple approach for a looooong time. Resorting to Dair eventually allows Sheik to start Ftilting(which I'm pretty sure trades with Nair anyway), which beats Dair. Fox could work on Bairs, but he can't outspace Sheik that well before a dash attack gets under his retreat.
Sheik can needle camp Fox too. Sheik just has to make use of the favorable diagonal angle that platforms provide(ban FD unless you tope chase well as Sheik durrr) to control Fox's approach.
Even if we say Fox camps harder, he has to approach Sheik at least somewhat directly in order to go past her. Fox is in a corner camping his butt off, which makes gimping easier. The point? Camping vs Sheik is extremely difficult to the point of not trying it. Fox camps, so now he will try to use platforms to escape, correct? Good luck getting past Sheik's Bair/Uair. It's possible, but it requires lots of precision and trickery.
Fox combos Sheik hard, wooo. Sheik only needs a few good reads on a Dthrow before a dash attack either sets up an easy tech chase(from CC) or dash attack/tilt to death combos. Needles and a few Dthrows/other hits push fox to a percent this works at fairly easily.
Fox rarely 0-deaths Sheik by the way. Sheik can get out of most of Fox's combos. Just go to the edge(gasp). By the way, Sheik has shino stall to recover effectively, and edgeguards Fox about as well as Fox edgeguards her. The difference? Sheik can get onstage vs Fox and reverse the situation way easier than Fox can do the same to Sheik. Sheik is like Marth in that a good dash dance by the edge game can spell doom for a spacie that slips up even a little bit, but this can also just happen due to a well timed edgehop WL to Bthrow.
-you can't CC the a fox nair, dair or bair because the fox will always shine before the sheiks move can come out (it has a 1 frame startup time right?) Plus low % down tilts are stupid anyways... the same for dsmash but only not so much because there's a chance the fox won't tech (if he does, it's a free hit or grab on sheik... at low %'s again)
-if you try to ftilt a fox approaching with nair, then you'll either lose out or trade hits. Neither as good for sheik because you take more damage from the nair than fox did from the ftilt, and he recovers faster. If fox is high % and you trade hits, sheik won't have enough time to finish the combo.
-trying to camp with needles isn't going to work if the fox is smart... he'll just start far enough away and ramp you back... and ACTUALLY tack on some % with lasers. Needles are only good for controlling the bottom platform on a stage for a limited space in the middle, but if you're camping the sheik into approaching you, that is worthless is worthless.
-the only thing sheik has in favor over fox is edgegaurding, and only slightly. Sheik has more options to try and gimp fox, but an experienced fox can avoid them a lot of the time. Sheiks up b is good if she can sweet spot the ledge... if not, her recovery time on landing on the stage is ****ing LONG. It's an easy up smash, grab-> up air, back air, or downsmash for the fox. So the answer to sheiks up-b is just edgehog and dont get up until you know her trajectory isnt the edge.
-Sheik is the PERFECT weight for fox's combos to work. She slides just far enough away from a shine to get grabed->upthrow->upaired, upsmashed or shined again (if you waveshine correctly) automatically. There's no escaping those combos unless the fox gets greedy or just ****s up. He has more options and a **** ton more "a-b-c combos" that work. Sheiks game relies on her ability to read the opponent.... which is a much harder task than just outpressuring the opponent like fox has to do. When fox gets dthrown, he has options, and the sheik has to react to them at almost the same time the fox makes them, in order to capitalize on the before the fox can re-react. A lot harder to do than just Nair shine nair shine nair shine.