Her weaknesses, without going in depth, are as follows.
- Crouch Canceling. Pretty much everyone loses to cc, but zss' punish game gets wrecked by holding down (even dsmash lol)
- Cannot combo fast fallers
- Marth syndrome. Combos into fair at relatively early %s, but after that cannot combo into fair against most characters. After that, he only kill option is basically back air which is very telegraphed.
- Can't kill off the top, making it hard to kill heavys (which is mostly fine, since she combos heavies well generally)
- TERRIBLE throws. Close to, if not the worst throws in the game.
- Pretty much all of her long ranged and really punishing moves come out super slow, giving your opponent time to dodge them on reaction, making them only good for hard reads. (in other words, he smashes and side-b are pretty bad all things considered)
- Relatively bad approach options, with only bair being truly safe on shield.
- Very light, so she dies early, and she doesn't get out of combos very well, Jason. She gets out of juggles from being above people, but down-b has too much startup to get out of combos.
- Has quite a few TERRIBLE matchups due to having very defined strengths and weaknesses.
- Her damage values are bad across of her moveset. She makes up for it by damage racking with combo strings, but that means her moves have low shield stun, but makes her suffer against fast fallers more.
- Fair is very unreliable as a kill move due to being a multihit. I'd love it if they just remove the first hit and just made the second hit come out 6-8 frames earlier. (I also really wish that her upsmash worked if you weren't standing still, and her side-b couldn't be inexplicably CC'd to like 160%, but whatever)
- Recovery is real bad in some matchups, mostly ones that have an option that covers all of her options, like mk and marth.
Overall, I put her at 40-60%, probably just over middle. Her moveset as a while is certainly below average, but a character that fast should have sub-par moveset.
As for the pros, I agree with @
Myst007_teh_newb
for the most part, minus the concluding paragraph, the down-b out of combos and the freedom of movement in neutral thing. She's top 5 easily, but I wouldn't say she's the best.