well, not bad, but currently the number one must have is a Winged Tyrant, two twin devourers: Brain Leeches, and a Thorax hive full of Electro-grubs 240 points of Awesome.
Most any list starts with one, then adds more as they become possible. The Haywire, and Vector Strike, and the massive shooting lets them solve most any problem.
A Tervigon is only a "Middle" choice currently, if you do use one, add a Thorax hive of Electro grubs.
Personally I would magnatise, or just build it as a Tyranofex, Acid Spray, and a Thorax hive: Electro. that's 185, and I often find the points for Adrenal Glands as well.

I find it a magical unit at low points, and a usefull unit at higher point levels.
Carnifexen can handle Vehicles in assault with a D3 HOW S9.
At least one source of Shrouding is pretty much a "must have" for Tyranids as well.

(A Venothrope, or Malanthrope)
Good luck! And welcome her to the Hive Mind!