#1 If you time them correctly it will hit her when she attempts to do anything but drop down and regrab the ledge.
"It will hit her when she attempts to do anything but drop down and regrab the ledge." Isn't that what planking is? I repeat, your needle tactic will not hit a planker. I will also state that this tactic easily allows ANY character to get back on stage with a roll. Needles are not her best option when they've already gotten the ledge. Learn to sh n-air.
#2 You underestimate the length of the Chain.
Also... if you are under 100% percents the Chain can hit you out of anything you do. This includes your ledge attack and snapping (the Zair thing where you regrab really fast).
If you really commit yourself to using the chain from that far away, there is nothing you can do to prevent a ledge drop->double jump away-> super missile. Thanks for the free damage.
If you're platform camping on BF with chain, it still applies because Samus can wall jump off the lip->any missile. Give me a video to prove otherwise that I'm overestimating the length of the chain.
The fact of the matter is, committing to using chain against a projectile user (who can easily abuse them off stage as well) is a bad idea.
Finally, if you commit to chain camping close range while Samus is under 100%, again, roll works. You will hit us when we're behind you for 5%... and then from there Samus has options. SH chain does not have enough hitstun to stop someone from punishing you from behind. As long as they SDI properly as to not get dragged in front of Sheik, it's a free hit for Samus.
EDIT: Looking back at the frame data, Samus is invincible on frames 1-24., ledge attack comes out on frame 25. If you're that close with chain, the ledge attack hits Sheik. Samus's hitbox will connect with Sheik's hurtbox on the same frame Sheik's chain hits Samus if you're close range. And, I'll repeat, if you're not close enough, can do nothing to stop a z-air from under the stage. A video would be nice to prove otherwise.
#3 Well, I guess you could simply refresh you invincibility frames.
Indeed, my good sir.
If you are under 100% Sheik will screw you.
I've already proven why edge-guarding Samus with chain does not work. It only works against certain characters and you know (or should already know) that.
If you are over 100% it is harder for Sheik to do things to you. So I say go Zelda. You are at high percents anyways so why not just let us Transform easily?
If you were planning to transform, you would have done so already, before Samus got hold of the ledge. Unless you're the type of person who transforms after a low knockback move... which I'd hope you're not.