Hello spacegirl: I noticed this is your first post here on PC. So... welcome to PsychCentral. We here on PC cannot offer psychiatric diagnoses. Our purpose here is to share experiences, exchange information, & provide one another with support. Perhaps some other members will have some thoughts they can share, though, based on their own experiences.

One other forum, here on PC, that may be of particular interest to you would be the partners of people & caregivers support forum. Here's a link:

https://forums.psychcentral.com/part...ivers-support/

And then here are links to 3 articles, from PsychCentral's archives, on helping someone who won't, or can't, help themselves the first by our host Dr. John Grohol, Psy.D. Next is 1 article on how to support a loved one who has a serious mental illness. And then there are links to 5 articles that take up the subject of dealing with someone who is delusional:

Denial is a Powerful Impediment to Treatment

11 Ways to Help a Loved One in Denial

How to Persuade Your Loved One to Seek Professional Help

15 Ways To Support a Loved One with Serious Mental Illness

https://blogs.psychcentral.com/careg...is-delusional/

https://blogs.psychcentral.com/careg...dium=popular17

https://blogs.psychcentral.com/careg...dium=popular17

https://blogs.psychcentral.com/careg...-to-delusions/

https://blogs.psychcentral.com/careg...dium=popular17

I wish there was something I could offer you here in the way of a path forward. You wrote that every doctor you've spoken to has been passive & uncaring or had no idea what was wrong. Your sister was even hospitalized for 10 days & the doctors there had no idea what was wrong. The only thing that occurs to me here is that perhaps you simply have yet to find the right psychiatrist. Unfortunately finding the right mental health professional can sometimes be a challenge. (Perhaps you might also consider having your sister see a mental health therapist if she's not already doing so.)

It may also be necessary, at some point, for either you, or your Dad, to seek guardianship of your sister if it gets to the point where she is unable to make decisions for herself. (You made brief mention of the fact she's still in college & apparently has a job though. So she presumably may not be at that point yet?)

Hopefully there will be some other members, here on PC, who will have some more useful suggestions to offer. In the meantime, here is a link to another article, from PsychCentral's archives, on the subject of psychotic depression. Perhaps this may be akin to what your sister is experiencing. I clearly don't know. Mental health diagnosis is a job for a mental health professional. But it's a thought:

https://psychcentral.com/lib/psychotic-depression/

My best wishes to you both.