Mentally ill sister won’t seek help

Location: Colorado, Maryland, New Hampshire

My sister lives in Colorado. She was recently arrested for a domestic violence charge and ordered out of the home until a following court date. Ahead of her court date, my mother went to Colorado to pick up my niece, given the unstable situation.

While in MD at my mother’s home, my niece’s first tooth came out. (She is 5 and both of her front teeth were previously very loose.) I cleaned and packaged the tooth to send back to my sister as a keepsake. When my sister saw the missing tooth she immediately began interrogating her daughter, asking who pulled out her tooth. She made the girl promise not to lose anymore teeth. When I told her that this was not healthy / normal behavior she accused me of harming her daughter. While also sending me pictures of where she has been re-affixing her daughter’s loose baby teeth with dental cement because she “can’t have her missing teeth” because “she has pageants” etc etc.

Many days of abuse / harassment has followed. She’s not mentally fit to have this child. This is one of hundreds of episodes, and I cannot take it anymore.

I am now back home in NH. How can I report her and ensure that someone in my family keeps custody of my niece? I don’t want her to end up in the foster system.

Is there some way to force the issue of a psych evaluation?

Thank you in advance.