I played her three times so I totally know what I'm talking about k.

Harrier - Doesn't seem all that great. It's a little too random since it tends to target random minions when you don't really want it to and it can mess up last hitting.

Blinding Assault - Damage seems a little lacklustre as a poke, but it does have the nice blind effect for trading. As a waveclear it's also not the best since it'll only hit one row of minions unless you make them bunch up and it only takes about 2/3 of their health. Terrible scaling.

Heightened Senses - This one's pretty good. 40% AS isn't bad at all and 80% AS during ult is ridiculous. The active is decent although I think Ashe's Hawkshot is better due to the range and much longer duration.

Vault - Good for initiation and ganks, especially during ult. It's okay for escaping but it's not really a true escape like 90 Caliber Net or Arcane Shift and it can backfire horribly. The guaranteed passive proc is very nice for trades/fights. Again, horrible scaling.

Tag Team - This is the most interesting skill and the hardest one to use properly. 80% movement speed is really good for initiating fights or ganks, chasing down enemies or for escaping from an area. The attack speed from W makes you a very strong duelist in melee range. The hardest part is finding a use for this in teamfights; as far as I can tell it's usually a bad idea to use this during a full teamfight unless you have something on your face and you're safe to just stand in melee range and duel them 1v1. Also this skill has an incredibly long cooldown for an ADC ult, it's pretty ridiculous and you really don't want to waste it.

Skystrike - Seems like a decent enough execute if you use the transform to engage and get someone low. I didn't really get much use out of this to be honest since I tended to either kill without needing it, die before having a chance to use it, or the enemy was already out of range for it.

Overall she seems like a strong early/mid game champ who excels in forcing small scale fights, dueling and catching people out. Due to her short range, poor scaling, lack of a proper escape and the difficulty with using her ult her late game seems to be very weak for an ADC. I think balance-wise she's pretty average, maybe a little on the weak side. She's pretty fun to play though.

Disclaimer: I could be totally wrong about all of this.