I'm sorry, but I dislike both Trinity and Jade very much. The combo has nice flow, but that's as positive as I can be about it.
Having a girl after two boys means you have the perfect opportunity to break out of your name pattern. After all, she's not like the kids who came before; her name doesn't need to echo theirs so closely. There's no need for you to restrict yourself to Tr- names.
You know, it's not my style, but I really enjoy the way Trinity Jade flows. I love the suggestion of Trinity Jane even more.
I think that Trinity can go a few different ways, as can Jade, but together they do seem a little hard-edged. My main concern, though, is how close it is to Tristan.
Trudy or Tracy are good options too. Tricia, again, is too close to Tristan.
Two's not an unbreakable pattern, and you can establish different patterns for boys and girls if you wish. How many kids do you think you're likely to have?
What other Tr names do you have lined up in case you choose to keep this going? Troy, Trent, Truman, and Trevor come to mind for any future boys.
I'm not a fan of Trinity at all, but I want to wholeheartedly second the suggestion of Tressa. It means "third," and it's almost completely undiscovered but still feels familiar.
Tristan, Travis, and Tressa I could get on board with. All three names start with a "tr," sure, but the first vowel sounds are different. You don't get that with Tristan, Travis, and Trinity.
I also wanted to add that you don't have to use a "tr" name for your daughter. My general rule is that two's a coincidence but three's a theme. If you plan to have more children and want to break the pattern, now's your chance.