Guardianship of foreign minor

I´m a naturalized US Citizen originally from Bolivia.

I came back to Bolivia for 2 years due to a family situation, and during this stay I was given guardianship of the 16-year old daughter of a family friend who became ill and can no longer care for the girl. She´s been living with me and my family for the past year and a half.

I´m now going back to the US with my family and would like to know how to legally take this girl with our family back to the US, as there are no adults able to care for her in Bolivia. I believe this could be treated as an extreme hardship situation, how can that be taken into consideration for immigration purposes?
What type of visa do we need to apply for her?

I know I can probably get her a tourist visa, but I would like to know if there´s is a "legal" way of proceeding so she can enroll in school and have a normal life in the US.

Adoption is not an option as it takes 2-3 years in Bolivia, and she´s currently 16.

Any help would be greatly appreciated. Thank you!