It's not a mental illness according to every major institute of psichiatry in the world, as it alone does not cause an impairment. There are kinds of dysphoria which are considered illnesses, for example, one where you recognise a limb as alien to your body and so you feel the need to cut it. What makes it an illness is that, if that wish was to be granted, that person would become invalid, meanwhile with gender dysphoria, thanks to the advanced tools we now have, it does not cause any impairment. It's not "mutilation" by definition, because it does not damage your body in any way. All it does is change how you pee and have sex.
I agree with you about the kids part, but here we are talking about an almost 30 year old woman.
With all that said, no, I don't think she's actually trans. I get questioning your gender identity (I hope she discovers something about herself), but we know how impulsive she is and all she's done is wear boyish clothes, cut her hair short and do fetish videos about it while refusing to take hormones or do any kind of surgery.