The early game is where she shines. Do not trade with the Sona unless necessary. Your range is smaller then the ranges of Sona because of your passive. Try to use the potions and the flasks, so she does not harass you out of your lane.

The mid game is where you can overshadow Sona the most. Try to pick up an urly Long Sword, that way you can last hit much more earier. If you have trouble with Sonas burst get the scepter, it will give you much sustain.
The first real item you have to get is the Black Clever. It is an very underestimated item and it can get that low armor number of Sona even lower. For now you can easely trade with her, and if you have a good support, even get a kill somtimes.

The second big item you have to buy is the Deathfire Grasp. Because you can easily use your W to initiate, the extra ability power can help you with your burst.
After your DG get the Gardian Angle. You have most of your damage items now, so a little defence won't hurt(you get it :3).
Zeke's is just a no-brainer.
Hurricane is great in team fights, lots of AoE damage.
Finally, Ravenous Hydra. Even though it is for melee only, the stats it gives are great for you.

Late game Tristana is one of the best late games there is. Just jump in with your W and start autoattacking. You will win the teamfight with ease.