She's called a sniper viper =) Basic principles for a ranged char applies. Load up on pd charms. Obtain CB, deadly strike from various sources. Use BoS to increase your attack speed.
A pus Spitter is a good weapon for this build with 250pd and 10%chance to cast lvl 1 lower resist. Other good bows/xbows will be weapons that either 1) have itd (kuko), piercing (buriza) or both (demon machine).
Using two +3shadow claws on switch for a +6 boost to skills.
Usually Venom and PD charms don't agree, as the PD charms damage is scaled down to the duration time of Venom (0,4 seconds) That does not leave a lot of damage, even from a 275 poison over 6 seconds charm
I read (in the stickies I think) about a build like that using a Widowmaker (ladder only). You get ITD, Deadly strike and GA for free.
I had one in 1.09 - she was using a Kuko before she died short of lvl 50. I never did get the Venom damage sorted out, and often just relied on Poison charms myself. Certainly not the best way to do damage... The Kuko is just an all-around good bow, but I had used Demon Machine earlier.
Other reasonable bows were the Zephyr runeword and Skystrike.