Accepting the Limitations of Supporting a Mentally Ill Sister

My sister is mentally ill and she has all kinds of distortions and false beliefs. It's aggravating listening to her talk about things and go against professional advice. Her own therapist told her that she needs more help than what her therapist can provide, but of course the therapist is wrong, and yet she still wants to see her. That's the only outpatient care that she needs.

The frustration and anger I feel towards her are immeasurable. I've been fighting so hard for her. Going against my family, being the only one supporting her and helping her get things done. I drove across the state to help her because no one that is close could get their shit together enough to be here for her. She's stupid and reckless and unreasonable but it's because she's severely mentally ill. I don't know how to talk to her. I don't know how to let some things go because I worry so much about the things she thinks she can do. I can see so clearly how her decisions will lead her back into a downward spiral and I have to accept that there is nothing I can do. It's hard to see her in so much denial and I feel this huge pit in my stomach because she's acting chipper and like she's all better when it will probably take her years and years to overcome the trauma she faced. I will let her make her decisions, she's an adult but it's tough to watch.
If we go around assessing people, judging them, based on what we think they could have done instead, then we will always be left disappointed.

It’s very often much more conducive to healthy relationships if we focus on what they have achieved.

None of us have lived our entire lives making great decisions.