I see Tristana as more focused on team-fighting and objective-taking than dueling with other ADCs. Her kit's more suited to being protected and doing area damage and doesn't quite have that effectiveness against really mobile damage dealers. That, and her damage is a bit delayed compared to most ADCs because her Explosive Shot takes some hits in to do its work.
If you lost a fight against her when you were that far ahead however, I think that's just a case of either straight-up losing a fight or getting caught in a REALLY bad position. Try to stick with the tanks on your team during fights and you should be fine.
Despite all that, I still think Vayne's too dominant right now and hope the do something about it soon.