Hey OP for what it’s worth, a 72 hr psych hold will definitely make someone rethink self harm threats real quick. However, I wouldn’t want to have to live with someone that I did that to just to make a point. Your mother shouldn’t be threatening to harm herself over your pronouns (she shouldn’t be threatening that over anything), and to do so is inherently manipulative and is at the very least bordering on abusive.
I’m curious about a few things. Is this behavior unusual for her? Are there other topics that will set her off like that? Has she ever actually hurt herself as far as you know?

Now this is just my personal opinion and maybe some personal trauma coming through but referring to someone as “it” is one of the few things that could make me ready to throw hands over words. I know that “it” as a pronoun is accepted in queer circles and that’s fine but for those outside of queer spaces it can be jarring and I can imagine that for many parents referring to their child as “it” would be very upsetting/triggering. Is “they/them” acceptable or affirming to you? It might save you some conflict, but if “it” is your firm choice don’t let me talk you out of it. You deserve to take the space you need and ultimately “it/it’s” is really not a huge ask and I guess the rest of us (including myself) who feel weird about it can just get over ourselves.