Vengeful Spirit is an easy hero to play as and a great support for countering tanky, high armor enemies. I recommend playing her in the safe lane. (Top for Dire, bottom for Radiant.) This build doesn't require very much farm to be effective and once you build a Mekansm, the rest of her item build is mostly situational. As for her skill build, max Magic Missle first for damage potential and the increased stun duration then Wave of Terror for the minus armor. Let me know how the build plays out for you!