Sheik is my best matchup (apparently) since most of my PR wins have come from sheiks. However, the matchup still feels very tough for me, I think its cause it takes the most mental fortitude. Here's my take on the matchup: stay grounded. When she full hops, she'll come down with a bair or fair, and if you try to challenge this, it makes it easy af for her to hit you. She wants to approach you diagonally. Your best opportunities to hit her are when you're both at equal vertical height, so you can approach her horizontally with a bair. Another advantageous position is below her. Up-air is super good, and seems underused by lower level puffs imo. If youre below sheik (w/o platform) her only options are dair or nair; dair sucks cause it lasts forever and is easy to punish, nair should be a free up-air for you, which will lead to more up-airs or rest. If you're below sheik while shes on a platform, its the same thing.. usually sheiks will just run off the platform and bair/fair, or drop down bair/fair, and you can up-air both of thses if you're positioned correctly. Generally when you're fighting sheik in neutral, you wanna mostly space bairs, and then cross-up the sheik with a nair every once in awhile.. usually you wanna land behind her, but if theyre scrub, you can land in front, stay crouched, and they will try to grab, which is free rest. Up-tilt is super ****ing good vs sheik, it's your best rest setup. Up-tilt can poke her shield if her feet are showing, or you can try to guess a jump oos. Nair->Auto-cancel->uptilt is good against sheiks who werent expecting to get hit by the nair, or try to act out of being hit immediately. Pound also leads to rests often, so if you are falling in the air and she is to without a double jump, sometimes you can sneak it in there. When a sheik needles from air, wd under and sometimes you can get an f-smash when she lands. Edguarding sheik is easy hard. When you knock her off, the first thing you try to read is her double jump, which if you hit should be the stock. If not the double jump, try to read her up-b (before she's invincible). If not either of these, grab ledge. From here you can react, if shes far off, you can hold ledge, if shes kinda close you can wait and rest her on stage, if shes super close, you might have to avoid her up-b hitbox, which is the only hard part imo. Regular getup from ledge is good for edgeguarding, especially when they go high. Final thought- usually you should back or forward throw, whichever knocks them off stage, but if youre in the middle you can down-throw. If the sheik DIs the down-throw IN, thats a free rest, but most will DI out, which on most stage lands them on a platform. Apparently its possible to react to any of their getup options and get a rest be positioning below their tech in place, and then quickly reacting to the techrolls.
Good luck! Hope some of this helped.