Adopt a foreigner who is older than me

I am in my 30s and I live in Virginia. When i was a few months old, my parents hired an au pair, 'Maria,' who is Ecuadorian. She lived with us and helped raise me till I went to college. She then returned to Ecuador to help her elderly parents. She would love to return to the US but never achieved proper residency or legal status. We talk often and I have been to visit her in Ecuador a few times. I consider her to be my second-mother.

Question: Is it possible for me to adopt her in order to bring her to the US? She is mentally competent, and though she is getting older, she is not disabled. I would be able to support her financially.