Hi OP.
I imagine that if she is saying she is trans she'll be in some echo chambers like on reddit.
Reddit is a really dangerous place because there are also detailed instructions on how to access the darknet on there and you can buy pretty much anything. I think I first got onto it around 14 years old and the things I saw horrified me.
However, at around 16 I also started taking testosterone, not because I was trans but because I was competitively into powerlifting, and there were a lot of websites that you didn't even need the darknet to access to buy these things from.
When my mum started getting wise, I used to just go to my local gym supplement shop and the dude who owned it would sell us gear under the table. I had no digital footprint for this, I just needed literal cash.
Whenever one of us was out, we'd say "Oh I'm going to so and sos does anyone need owt?" and then we'd just collect it when we all met up from whichever person had been to the shop.
There are so many places to access it, gels, injectables, pills, and loads of online unregulated forums that tell you exactly how to dose.
I stopped when I was 18 when I developed a pulmonary embolism, and also had a small heart related event, never officially diagnosed as a heart attack but spent 2 weeks flipping between the acute medical unit and cardiology.
Looking back, I feel so stupid, but I'm disgusted how easy it was to acquire this stuff. I nearly died.
DB's partner is also a trans man, much younger than I am, now 18 so going through proper channels, but before 18 she was also just acquiring testosterone through similar unregulated channels.
The problem is with people spouting "better a trans kid than a dead kid", is that the whole medical transitioning process is experimental at best, and forums online are full of misinformation that is equally as likely to cause significant bodily harm if not, like almost my case, death.
I really deeply believe that for some trans people, like your daughter, it is an all consuming mental illness, that we're not allowed to mention. Like the emperors new clothes. Naming it just gives them more fuel for their fire, and so it's incredibly difficult to get them to see the bigger picture. It is delusions that they insist you play an active role in otherwise you're transphobic, and as soon as they utter that word all trust is gone and it's nigh on impossible to win them over.
If you remove the sachets, to you and the rest of us, it's because you'd be trying to keep her safe, but to her it would be because you're transphobic.
I think you need some proper medical advice from a medical professional to focus on harm reduction. I don't want anyone to go through what I went through. It was ignorance and arrogance on my part and I didn't want to believe it could happen to me.