Honestly probably not but let me lay out some evidence that I have collected from the two minutes of film shown in the trailer.
First, make note of child Katie’s t-shirt.
It is a bright red color. Anyone who has shopped for young children will know that most young girl’s clothing is made in shades of pink, white, yellow, and maybe pale blue. Bright saturated colors like her t-shirt are more commonly found in boy’s clothing.
This is not a hard and fast rule and there is no reason her parents couldn’t have bought the t-shirt from the boy’s section. Also, I realize child Katie’s t-shirt is the same color as young adult Katie’s jacket as part of her overall character design.
Second, take note that her hair is fairly short but a small section is pulled into a very short pony tail.
It does not appear that an adult has brushed her hair and pulled it into a ponytail. It is off center like a child did it. Is this a young trans girl attempting to express her gender? The small pony tail appears throughout the videotape scenes but Katie’s hair doesn’t get longer despite the scenes covering four years suggesting her parents kept her hair short.
Third, while reminiscing about their relationship during her childhood, Katie’s dad refers to her as his “little buddy” and “killer”. While neither term is exclusive to young boys, there is a distinct lack of girly nicknames or terms of endearments in these past scenes
Fourth, Katie’s phone and laptop have her name prominently displayed on them. Perhaps to remind her family of her new name?
To trans people the names we choose for ourselves are important. Personally I can recall how happy I felt seeing my name-tag display my real name. Also in the years before I could come out I would write my name in notebooks just to see it.
Obviously cis people can write their names on their possessions. Another thing to note is the “Hello my name is” sticker on her laptop which is probably also a nod to Spider-man: Into the Spider-verse in which Miles used as mini-art pieces.
Fifth, throughout the trailer two symbols are heavily associated with Katie: rainbows and lightning bolts.
Katie’s brother’s main symbol is dinosaurs. He wears a dinosaur t-shirt, his phone case is a dinosaur, and his cup has dinosaurs on it.
But his cup also has lightning bolts on it. Could this cup be a hand me down from Katie? This cup could just be the bother’s but when considering the thought and planning that goes into designing themes and color palates for animated characters it seems odd to mix symbols from two characters on this cup. It’s not impossible for a little girl to have a dinosaurs and lightning bolts cup but it does blur gender lines.
In conclusion, Katie may or may not be transgender but there is enough circumstantial evidence in this short trailer for me to make this post. How much more evidence will be revealed in the actual film?