Philippine identified adoption

We live in the United States and have been sponsoring a little girl in the Philippines for the last 3 years. Her father is deceased and her mother has never been involved in her life. She has been raised by her fraternal grandmother since birth. The girl is now almost 8 years old. Her grandmother had been ill, but seems ok now, although she is unable to work. We've discussed adopting the little girl with the grandmother to ensure the girl's future. We would love to do this and the grandmother would love for us to, as would the little girl. A couple of sources have told us that this type of adoption is not possible from the Philippines. They said that the local adoption board would never approve it. We've reached out to the board but they haven't responded to our emails. Does anybody know? If it is possible, what steps do we need to take to achieve that as quickly as possible? If this type of adoption is not possible, is there any way we can be named as the girl's guardians should something happen to the girl's grandmother? We don't want her to end up with nobody to care for her. We want to help, but we just don't know the local rules.