oh.
i thought she had needles for that.
if her needles didn't angle downward, i feel like that'd be a lot more of a problem. but since they do...meh, maybe it's just cause i play ganon, so i'm RARELY able to get below the *****.
Nah, needles don't really get the job done. They only go diagonal, and if she doesn't have a pretty big store of them they aren't much help, anyways. Diagonal needles are by far the best from platforms, but doing short/full hop needles is really easily baitable/punishable.
Yeah, like Josh said, most floaties are pretty bad from above, but a combination of things makes it by far the worst for sheik. Since sheik's jump is super high and she is floaty, any time you jump into the air, you are going to be there for a long time (unless you land on a platform).
This leads to two problems. Some characters, especially fox, can just run up under her when she jumps because it takes so long and hit her. This makes it so that Sheiks have to be very wary of jumping into the air, which leads into the second problem: stage control. Since she has to remain grounded a lot of the time, it's pretty hard for her to use aerials to get people into their shields. When she jumps, the opponent has more time to augment their spacing to make it bad for sheik than they do vs. other good characters. This is why an Amsah style sheik that relies on a lot of aerials can only work if you really have your opponents number. On top of this, all of her tilts are ccable until around 60/70 percent, so her only tools vs. a low percent opponent are needles, grab, and utilizing platform wavelands to avoid her jump height weakness (the shorter the platform the better it helps, which is just another reason why sheik is good on Yoshis/FoD).
So at low to mid levels of play, Sheik is really easy to play. She has easy combos and pretty straightforward edgeguarding. Players aren't good enough to take advantage of her big weakness and not consistent enough to avoid her amazing/easy punishment game. This results in two main styles of Sheik at high level.
The safer way to play Sheik is to stay grounded most of the time, use really good spacing/precision to bait aerials and get grabs (which is difficult because her dash dance sucks), and to capitalize heavily on mistakes. This is usually how m2k plays, which is why you see him staying near the edge so much; he gets a few hits either from a mistake or with good spacing and usually takes a stock.
The other way to play sheik is the amsah way. Get into the head of the opponent, condition them not to punish your jump, and then abuse sheik's really good aerials/combos/everything.
Then there is the kdj style which mixes the two in an amazingly beautiful way.
Don't get me wrong, sheik is amazing, but I just think her weakness is really glaring. Fortunately, her strengths are too.