How is your sister able to finance an office visit with her pdoc? Were she to get SSI, she would then automatically get full Medicaid.

If the pdoc prescribes a med for he/she, as he surely will, your mom could ask to see the bottle of pills. There is no good way to ascertain if she takes the meds as prescribed. From what I've read, a lot of people who are put on Abilify end up being non-compliant. I'm not sure why that is. Comliance is hard to monitor. It's not that hard to learn how to appear to swallow a pill and then regurgitate it.

I see above that you say your sister is currently drinking. Is she content to sit at home drinking, or is she out finding drinking companions. How is she financing the drinking?

Since your sister is age 30 and you are a year younger. I take it that your mother is not 85 y.o. or even 65 y.o. You mom is in the prime of her life, at a point where her own mental faculties are at their peak. Deciding what to do about your sister is really more up to her than it is up to you. You describe your mom as "passive." It sounds to me like she enables your sister's bad behavior by being too tolerant. A lot of what's going on here is between the two of them. There may actually be very little that you can do to affect what is going on in that household.

At some point, if your sister comes to the attention of a court, as a person in need of a legal guardian, your mother (or you) may not be the person best suited to take on that role. If a guardian is needed to consent to treatment that your sister doesn't want, I think it's wiser to let a party outside the family perform that function. Why set things up that will only lead to your sister being mad at your mother? At one point my brother asked if I would be willing to be his legal guardian because he believed I would never consent to anything he didn't want. Since that was his expectation, I resolved that I would absolutely never agree to be his guardian. Why should I have him mad at me?

Being mentally ill is one of your sister's problems. She has other problems. She is a substance abuser. She is prone to hostility. She is dishonest. She keeps company with unsavory characters. This all points to her being a person who, at age 30, is already permanently damaged. She is damaged emotionally, and she is damaged in her character. She will be the bane of your mother's existence for as long as she lives in your mother's house. The sister you used to know is not coming back.

Your mother might want to consider putting a secure lock on her own bedroom door. This would give her a safe place to retreat to, if your sister became threatening.

I also think your mom might want to make a report to Adult Protection Services. A social worker from that agency might help her to more clearly see what options/resources there are for getting your sister help and how to access them. You want to get started on establishing a paper trail raising the concern that your sister is mentally disturbed.