Bringing my mom's mentally ill sister legally into the country? Please read?

I will try and keep this as short as possible so please bare with me:
My mom has a sister in Mexico, who for all of her life has had no health issues at all. She was in perfect health condition actually, but a year ago, she started showing signs of a mental disease. She is considered "insane" and is in terrible trouble in her home village where she faces repeated persecution and her life is in danger. None of my mom's relatives in mexico want to care/take my aunt to a mental asylum even if we pay for it. So my mom wants to bring her here to the states where she would provide shelter/pay for all medical expenses for her. My mom was born here and is a U.S citizen but her sister was born in Mexico and therefore is a mexican citizen. We want to bring her here as soon as possible her life really is in danger, she wanders around the streets at night not knowing who she is she never posed a threat to anyone but is still persecuted. What can we do so that we can legally bring her to the states and give her residency or a visa? thank you soo much!!!