What ever happens, make sure she has gender dysphoria. Transitioning without dysphoria is a massive mistake, and most realize this sooner or later. If she actually is transgender, then transitioning is necessary for the dysphoria. She needs to see a psychiatrist/psychologist for a diagnosis, and it's important she does not lie/use examples on the internet of dysphoria to try and get a false diagnosis (this is what many non-dysphoria trans people do to get HRT/transition, as some places require a diagnosis first.) Make sure it's a psychiatrist/psychologist that has a speciality in gender dysphoria, as not all have. Getting them tested for autism is also necessary in my opinion. This is because a child can easily trick themself into thinking they SHOULD be feeling something, when they aren't, and therefore convince themself they are transgender/have dysphoria. In this case, it seems like lying but they genuinely do not know. It is possible to have gender dysphoria AND autism, but it is a risk.
The biggest mistake a parent can make is not accepting their child as transgender, if they really are transgender. That and as the answer above says, puberty.
There are signs your child could be transgender, but they're not black/white so I'll talk about them here:
- Interest in the opposite gender's clothing
- Most friends are of the opposite gender, rather than the birth gender
- Negative reaction to the birth gender's pronouns, in your case not wanting to be called she
- Hobbies that seem to not match their birth gender's
- A tendancy towards short haircuts, for this case
- Dislike of their name, if it's not a unisex name
- Dislike of their genitals
Childhood trauma is kind of a red flag. It means they could not be transgender, and are only using their transgender identity to try and escape from the trauma. Of course it is possible to have gender dysphoria and have had trauma, but it is worth considering.
I happen to have a few transgender friends, so please do not hesitate to ask any questions.