I like the rework, having always a low cool down on the E is really good, and seems well balanced because is not worth spamming it on a non poisoned enemy.The passive is nice,i love kite mages and she is "swifty". I really like the rework overall, for what we saw until now.
Some problems, in my opinion, are, in early game boots are quite good, most of the time is a cheap item that gives to you some Mov.Speed INSTANTLY (and not per level) and also some magic penetration/CDR (in some cases you take Swiftness or even Mercury, but you normally go for Ionan's or Magic pen boots), but this is the minor problem for me, she can't buy instantly some boots but you can forgot it and use money for other items and you still have the move speed some levels later on(also we don't know how much move speed she will get and how is it going to scale), so i'm ok with that. The only real problem i found is that enchantments on boots are quite strong, alacrity is cool on a kite mage, distortion is nice, and even furor could be good cause proc on single target spells. Maybe you should give to Cassio the possibility to build boots enchantment as a "passive buff", you can buy those enchantment when you want(or maybe after level 6/9) but they get displayed on your passive(and on the buff/debuff bar, so both enemies and allies can know if you have an enchantment) and they don't go in the inventory. You can have only one of them at time, they can't be sealed, and if you want to change enchantment you pay a little bit of gold.
If there are some bad grammar mistakes i'm sorry :D