I'm currently writing an edgeguarding guide that I'll probably finish this weekend, but I have the sheik portion completely done. I'm better at edgeguarding marth, peach, and spacies than sheik, but my edgeguarding against sheik is still probably better than my combo or neutral game. Hope this helps-
Falco can't edgeguard sheik especially well, but edgeguarding her is especially simple compared to edgeguarding other characters with falco.
If they're below you.
If they don't have a jump, you can go out there and back air her before her invincibility starts(which takes 20-25 frames, but Idk exactly how long) .If she does have jump she'll jump fair you, grab ledge, then make you sad, so I would suggest not doing that, unless you have bigger balls than Evil Knievel. If you want a big punish off the standard grab ledge edge guard for sheik, you need to read. If you think she goes ledge, just hold on. If you think she's going on stage, you can roll, and fsmash her back towards the ledge. Otherwise you'll probably just get a dair/dtilt into combo or something. Also, if you snipe her really well with lasers, you will basically force her to go low to recover. Once you do that, you're option open up quite a bit. You can do invincible ledge drop double jump bairs and invincible ledge drop shine bairs. Sheik can do very little to stop both of those, so she'll probably recover really low, and will be too low to double jump up b down to the ledge, which means she'll be vulnerable if she tries to go ledge, so you can just stand on stage and dair if she goes ledge, and dsmash if she goes stage. Once sheiks realize that they're screwed if they go low, they'll go high and take the lasers. you can take away their jump with laser if you read when they do it, then can go out there and bair her.