She has more damage than most mages and at the same time more mobility than most assasins, while having aoe, a slow and snare, low cooldowns, no real mana issues, being slippy due to her passive (on top of her mobility).
She is strong at any stage of the game from level 2 onwards. She has huge pressure in lane, she can roam very well, she can one shot people in mid game and she can half-shot people in lategame. Her w is impossible to dodge without flash/a blink. She does crazy damage and is impossible to catch. Yet they still haven't nerfed her? (the silence removal was a while ago)