While there's a lot to be said in regards to trans criminals gender-typical behaviour, I find the conservative "look, trans shooter!" finger-pointing so laughably ironic, given just how much death and straight up terrorism their precious white male supremacism directly leads to, and given how much their no-questions-asked gun-worshipping keeps these things in the news.

As for my opinion, based on limited info and my experience with social trends in this area, she seemed to have been the standard-issue awkward (probably autistic) terminally-online artsy animal-idolising female millenial (mentally teen) with an interest in horror and morbidity, perhaps with a crushing-on-mass-murderers phase. I've pretty consistently seen those women directed into the trans pipeline. She would've been told that her fascination with male fictional/real life killers and her not wanting to be feminine was due to her being male herself, which is in line with trans people's very artificial obsessive ideas about the opposite sex. Since she was probably around male-dominated horror/gore websites or 4chan-like imageboards, she might've latched onto things like guns, atheism-as-an-identity and the "kids are annoying and need to die" mentality, and might've pushed it to prove to herself she belongs there. She sure as hell wouldn't latch onto the misogynistic abuse-and-rape-women aspect of these communities since that would hit a bit too close to home (err, I mean it would "gender invalidate her") and also target her female friends, so she'd need to compensate with something else.

I'm not sure if she got roped into some 4chan-level trans crowd or transmedicalists or whatever, or if she was just going off of the ever-present patriarchal toxicity all around us. Either way she probably felt this would be an ideal way to gender validate herself as a cool edgy loner boy, which is more attractive than crazy hysterical bitch or some other misogynistic slur. She must've liked the idea, based on previous trans shooters and general trans crime coverage, that the news would have to refer to her with male pronouns. Heck, the trans crowd is already gender-affirming themselves with her - "See! Female trans people are just as violent as men because they are real men!". I really don't think testosterone would make that much of an impact even if it was involved (I usually just see it more intensely fueling and encouraging the degree of a delusion, but not really changing anything in an of itself), but for both this and the Colorado shooter, as far as I know they weren't even on it, so it's kinda funny to see trans activists scramble to gender-validate their stage of transition by claiming this is just another example of extreme totally-cis-like male behaviour. Trans identified women have completely different motivations for imitating male toxicity than men, who never knew any better nor were policed or held to a higher standard. They are active imitators, as opposed to male shooters and male trans people snapping because that's what they are used to doing when they don't get their way. Trans identified women are not gonna go out and impulsively rape and murder (unless they're schizophrenic), they're gonna try to act out a fictional image of a "dude" that will maximise their validation points. They're like robots imitating humans in that way.

If the woman has male friends, she's going to engage in a lot of asskissing to gender-validate herself, but she'll also know to keep her head down so the guys wouldn't withdraw their approval. I doubt a woman like that would end up as a shooter. She's either going to know her place, or eventually her bros will turn on her for being female but in a way where she ultimately won't be able to "not like other girls"-herself out of it. And you can bet they won't have much patience for her "I'm a real boy"-pronouns if they're even slightly edgy. She'd either put up with being creeped on, or she'd be traumatised and run off. Either way, she's not going to shoot up a school, because women don't do that out of the blue. If she's going to shoot up a school, it's going to be fueled mainly by gender-affirmation, as opposed to just lashing out.

The shooter didn't seem to have male friends, but she probably spent lots of time in male-dominated spaces. Whether those had a trans community, I don't know. The more dysfunctional (talking 4chan levels) trans communities tend to be male dominated with the usual gamut of misogyny, racism and male narcissism, and with male-identified women who are there for validation points from roleplaying as edgy guys, ironically in a community where said edgy attitude is maintained by guys identifying as women. So, that dynamic is par for the course, but I feel the difference is that normally, women in non-trans communities will try really super hard to distance themselves from any "politics" for maximum approval from men, and will hyperfocus or derail to whatever "apolitical" interest removes the focus from them being women (with male friends, misogyny would be pretty much obligatory on top of that). She didn't seem to be trying that hard at transitioning, which could suggest a more passive attitude she'd have to take on in non-trans communities in order to not draw attention to herself, meaning she'd try to compensate with more violent attitudes.

The trans activist types will be a lot more into gender-validating themselves through general conceptual ideas on gender roles and/or brainsex, as opposed to ass-kissing specific irl guys in exchange for "one of the boys" points. It's more ideological in that way. They can also try to win points by emulating extreme misogyny if they latch onto brainsex (everpresent in any male community), but in this case it's more a performance to convince themselves personally of it, than the irl guys around them who are grading their performance. Basically they'll do it not out of fear that the guys will turn on them, but because they want to assure themselves that they're naturally just as misogynistic as the image of a guy they're imitating, despite what online naysayers claim. This is a very common sentiment in female trans spaces, so if the shooter was in trans spaces this might've inflated the (not that unusual for her demographic) fascination with school shooters and push to stand out by imitating them.