She is not that weak if you can do her combo perfectly, she just lack of a proper role.
She have assassins tools, but buidling damage is pointless;poor scaling, can't put her damages fast enought before she get blown up.
She lack of utility as a mpen-tank; she get only one stun, while real tanks get way more ccs.
With some tweaks , she could be pretty good again.
Passive : Give back some HP to the spiderlings , but make them take more damage agains monsters
Q : Put a flat damage ratio (human) (0,4 Damage / 1AP )
Increase the %Missinghp ratio (spider) (currently : 3% / 100AP) -> ( 5% / 100AP)
Z : Add a small dot on her Z and make the spider scale a bit with bonus MS (30/35/40/45/50%) (human)
Increase the damage on-hit by the spiderlings whe Z is active (spider) (40/60/80/100%)
E: Make her rappel faster / more responsive. (spider)
R : Give her a bit of tenacity in spider form (20% ?) so she can build mpboots
(Could need some testing, maybe a bit too much buffs)