WHAT?!

Anyway, I'm really sorry for the loss of your bird. I know that pets can be really good friends. I'm also sorry that you find yourself in this situation, which is not something that you should ever have to "handle" at your age.

In fact, at any age, you wouldn't be able to fix things for her. She needs to fix things herself, being an adult, and the first step to take would be to see a doctor. Since you've recommended this multiple times (and indeed it's just common sense) and she has angrily refused, it seems safe to say that she won't do it - and definitely not at your behest.

She is going to keep on doing exactly what she's doing. You also cannot make her stop using unsafe chemicals on herself and on the house. If you take them away, she will just buy more, and probably threaten to disown you again.

Since you cannot change her behavior, I would recommend changing your own (I say this in the most uncritical way possible, since you seem mature beyond your years and I'm sure you take responsibility for yourself already). I very strongly suggest that you move out. Take the bird with you. Sure, maybe it's technically hers or your brother's, but they can't do much to stop you - just don't give any warning that you're taking the bird if you think they might. It's probably only a matter of time before she starts harming the new bird as well.

In the meantime, I agree with the suggestion to keep the bird in your room and get a padlock for your door! If she sulks or rages, ignore her. She is probably not physically capable of overpowering you at this point, and she will resort guilt-tripping or yelling. Don't listen.

You may repeat to her, while you're moving out and afterward, that you're happy to help her arrange a doctor's appointment. That's really the only thing you can do, if she'll let you - it's what she needs.

I agree that you should encourage your brother to try and get insurance money from the car accidents. It's very sad to hear that he'll probably be disabled. There is indeed a good chance that he's gotten in so many accidents recently because home life is very stressful. If you guys are close, you may want to encourage him to move out too.

Good luck!