My sister-in-law works for a non-profit that is a 501(c)3 in the US but operates in Ecuador. We have invited her here to the US and would like to apply for a religious visa exemption. Her purpose in the states would be to volunteer/work at schools and daycares to grow in her knowledge and ultimately be able to better serve the nonprofit. She currently has a 10-year tourist visa. We were told to invite her here for 3-4 months, then apply for the religious visa. The nonprofit would be the sponsoring organization, but since she would be volunteering, she would not technically work here or for the organization. Is this possible? Can anyone provide any guidance/assistance on how best to achieve this? She is also the sister of my wife so we could apply for her green card but she can't wait here while it is processed so we prefer the religious visa.