Rek'sai is a girl.
Also, if you're dying that quickly to a level 5 Zed, you should probably stop trying to fight a level 5 Zed with a level 3-4 Rek'sai. Junglers get way less EXP early on, and a zed with a level or two up on you will destroy you. Rek'sai also has very decent damage early on. Your burst combo consists of Knock up with W > Auto Attacking > Q RIGHT AFTER successfully landing the first auto attack > Finish the rest of the Q while staying on top of the enemy > E.
Now, you'll have to note that this burst pattern is good, but it can't outright kill from full health. That's why you should seek to invade the enemy jungler while they are low from clearing. You'll NEVER kill any of the laners by your self, but Rek'sai is one of the best invaders with her E. The only thing is knowing who you're jungling against. You'll probably never kill a Nunu, but killing a Kha'zix is well within your abilities