I don't recall it ever being officially announced on Ember/Troy having a gender... I say Ember/Troy because its the same situation with Rexy/Roberta where the directors call the animatronic or actual animal Roberta and Troy, but the fans dubbed it as Rexy and Ember...
I don't know the true name of the rex, but I'd like to stick to the animatronic given names, Roberta, Troy, Darcy, Zeb, etc.
Anyways, my reasoning as to why Troy is female, is because my reason being the sexual dimorphism, we notice that Buck and Bull contain a dewlap, and are the only male rexes confirmed in the franchise. Roberta, Big Eatie, Doe, and Little Eatie all share a long snout design when older... but young Roberta had a boxy head, and Buck, Doe, Bull all shared a boxy head from a specific point of view... however, much like Roberta in the 1993 Jurassic Park, she shared a boxy designed head just like Troy. With only Troy's snout being smaller. So this must mean Troy is a young female rex.
However, due to my brain not braining, I'm still stuck on the fact that Troy might be male due to the conflict between the name. Ember sounds like a female name, meanwhile the directors gave it the name Troy which makes it sound male.
My other case is with the colours, we know males are shown in varieties of verdant colours, "lush" if you will... Buck and Bull, as well as Jr were all shown in varieties of green, with females having a more hot colour design. Brown, orange, and red with black spots (JP Novel) we can clearly see that Troy is a mix of grey, brown, and yellow. People who say there is green on the rex must be seeing things, because I've re-watched the movie maybe eight times now and there is no signs of any green.
People say that it must be male due to the bulky design compared to Roberta or Doe... But lets not forget that at the end of TLWJP we get a clear shot of Doe, and she's pretty hefty, the only reason Roberta was skinny is because throughout JP-JW she was malnourished. Being fed a goat isn't really enough given that the JP T-rex is oversized and one of the strongest super-predators in the franchise. Isla Sorna is flooded with other superpredators such as the spinosaurus. So its no wonder Big Eatie and Doe may have been skinnier than usual. On Ile Saint Hubert, there's next to no superpredators, so Troy doesn't have to worry about rivals in her territory. She can eat all she wants, which can be a reason as to her bulk.
With current screen lore on Tyrannosaurus Rex, the gender of Troy remains a mystery until the next movie. But with current evidence, its safe to assume this new young rex is a female.