I clicked thanks to the information about the NY system. I read it, informational, non judging.

It's tough to be involved in custody battles, of any kind. Emotional sensitivity rises. Most of the states follow a standard system, all states do, a couple have extra measuring tools that include international laws as primary difference.

I feel most systems desire the nuclear biological family in tact, and the guardian's be either of the parents.
The fact you are making strides in recovery and under care, speaks volumes, is how I feel, personally and the perspective I read the words above, covering legality in wording, imo.

It's easier said than done, to not let another's motives, as your former sister in law, eat at you, it's necessary to come accross, clear, direct, sincere, unaffected by the experience.

Hope all turns out in your favor, keep us posted.