Mm. Good luck on your things, and I hope you're doing well, but I'm a little surprised nobody's mentioned yet that your passiveness is making things worse.
Humans are really, really social creatures, so they tend to get ENRAGED when they can't get social feedback. You already know how important social stuff is because you care really deeply about what people think of you, and some more than others; now remember that other people get those sorts of feelings also, but not just along rejection/support lines. The fact that your mother's son is, like, pretending to be a girl or something is likely a source of a great many not-nice feelings for her, but it wouldn't surprise me if the fact that she can't really talk to you about it is the more serious issue.
Like, the legality thing. Wrong direction to go in; it's not relevant to anything. If you found out it was perfectly legal for her to throw your stuff out, you wouldn't change your mind and decide she was being reasonable; so why would she do the same if you proved to her that it was illegal? The problem is entirely between you and her, and you should address it as such. Most people respond much, much better (or at least, more meaningfully) to direct personal challenges than accusations that they did something arbitrarily "wrong." The personal challenge thing is also something you're somewhat familiar with, because it sounds like losing or regaining the books was an entirely secondary issue to your mother throwing them out or your other family repurchasing them for you. Materially, the issue was trivial; socially, they were incredibly significant messages from the individuals in question, and that's what was important to you.
The "several days to respond" thing is really the poster child, though. I don't doubt it's easier for you, but I also don't doubt it's absolutely infuriating to attempt to have a conversation with someone, especially about something important to you, only to have them refuse to answer for another five days. It probably feels to her like you're scurrying away to avoid the issue, which is incredibly frustrating.
So... I realize you don't like confrontation, and I can't say it wouldn't be painful, but I'd still recommend you avoid avoiding her. When you have a problem with her, challenge her on it. Even if she blows you off or disagrees vehemently with what you have to say, she'll still feel the pressure of it and be somewhat more inclined to back off and respect you as a person. Remember also that changing your mind on things sometimes takes time, so even if she disagrees or refuses on the spot, she might keep chewing on it afterwards.
In the best-case scenario, this might even lend more credence or comfort to her perception of your condition(s), since it'll look less to her like you're collapsing in on yourself and turning strange and more like you're a functional person with some difficult to understand information. Having someone look you in the eyes and tell you something is much, much more persuasive than having them curl into a ball while muttering it.
And even if you do just bail out and never speak to her again, it'll be good practice and you can say you tried. Everyone likes and pays attention to contact, and knowing how to project yourself as a social force is an important skill.