and to have your problems/mental issues(i dunno how anxiety and ADHD fit on that list) and people around you too...well it is a shitfest of everyone hurting inwardly constantly even if people who caused issues are not present almost never. so that sole enviroment sadly ain't helping to heal anyone, but at the same time I'd say neither of you has time/place/money to get some better help or isolation in specialised place with medical professionals. Thou even when one gets that then they will guide you how to live in outside world where you won't be isolated nor protected so if person only seeks protection from anything even slightly bad at all times and expects the world to provide it then ehhhhhhhhhhhhhhhhh well it ain't realistic ;-; thou on positive note of tougheing up-being able to work trhough some of your probems or make progress on them lifts up morale and overall mood ^^
um, my advice would be, try to see if your sister think she is the only one with problems and as such should be treated as drop of water on a palm of a hand (cause as stated we all have problems and noone can escape them all, life has it's bad parts, but by getting through them we get to good ones) and if yes try to change or tell her that that is not the case and more importanty that time/life won't wait on her to heal sadly, she, for now, has to live with her illness/problems and it won't be perfect, but it won't be as horrible nor empty as not living at all, but pausing in time and space, focusing on present problems only.
Also it might help if you all on your own or together have notebook in which every evening you write down 3 bad things of that day and then 3 good things about that day-even if it is something simple-just to keep perspective healthy that it is not all rain and clouds,that there is good. I think it is good practice cause....well as we can see on news and TV most of it are disatsers and that can negtively affect people's mental health-global depression of sorts-it is more complicated then that, but the point is, if you are too exposed to only good or only bad inormation/situations your perspective shifts from realistic one and it can lead to other problems-keeping balance is importnat.
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this hurts to write and it will hurt you to read thou it is but a senctence-do not be surprised or take it too personally if when you point out she is destroying her realtions to people that care about her that she says she does not care about anything or anyone and that it is okay with her-it...at times it can seem like it to people, like nothing matters, or they say that to get people away from them cause they think they are bad influence and everything woud be better if they never existed. I can continue on this note later if you want me to,okay? Know that none of that is true, it is longtime hurting speaking, not really her.