1v1 she's gonna be hard to engaged. She can dodge towers pretty well since she has good range on her ult and awsome burst.
The ult it-self doesnt hit that hard unless you factor in you can do it 3 times in a row. What really hurts is the ult + Q + auto attack and the fact you cant get away from her.
In team fight she dies really quickly to focus or CC. Her invis is usually easy to counter as an escape if your in team. You can use wild card and shoot thru her Shroud, might hit her.
But if you get in range of her ult and dont have good HP, she will kill you almost instantly.
Backdooring is going behind the flow of creep to destroy structures. Alot of champs are better at it then her.
edit: She is VERY squishy, like eve she has low base HP/armor/MR, low per lvl HP/armor/MR.
I personnally start (like pheaks) with 2 HP quint + doloran's blade, so it giver her almost 700 hp starting the game. Keep in mind that when i play other champs, i start with 3 HP Quint and a doloran something.
She doesnt look that squishy cause most players build her Railey specter and/or mallet and/or haunting guise. But she lacks armor and MR (even with mercs) and she cant retreat well from combat.
Like any assasin, if you feed her, she will rape faces.
re-edit: TF is a good counter for her cause he has a stun, by the time she's out of the stun she will be dead in team fights. 1v1, at equal strenth, she should 1/2 your hp before you can get a gold card. And 1/2 the rest once the stun is over.
one more thing: Becarefull when she runs away, she might be cycling her CD to charge back. Same thing with Shround.