Firstly, she HAS 2 abilities that can get her out (NOT counting summoner spells). her ult which can be used 3 times, and t-shroud.
Instead of placing the t-shroud directly in the middle of the lane to get away, try using it on or near bushes, and then EASILY juke who ever is chasing you. I've gotten away from entire teams by t-shrouding near a bush, then using her ult on a neutral, if you can't get away using that.... then perhaps a different champion would be better.
dont forget, she is complete burst. juke them, when they turn to run, pick one off and repeat. she has such low cooldowns, and such high burst, as well as pretty decent survivability, you need to make CORRECT use of her abilities.