Can you help me with my questions about becoming a "godmother"?

I understand the meaning of a godparent in the eyes of the Catholic church. I, however, am not Catholic. I am baptized in a Christian church but I am not practicing. I have many different views; I am incredibly spiritual and believe in being a good person. I practice being a good person. I have researched and talked to people from all over the world that have different religions and beliefs; I find it fascinating to learn so many different views. I believe in being kind and treating people with respect. I believe in loving yourself and others as well as the Earth. My very best friend and her husband would like me to be their new daughter's godmother. My best friend and her husband are not practicing Catholics but are both baptized as such. The husband's family are very devout Catholics and are making sure their baby is baptized etc. I would love to take the role of being Godmother, but I can't be what the Catholic term defines as a Godmother. My best friend and her husband want me to be fully involved in their baby girl's life as well as if something happens to them, I would be the one that umes the role as parent. I know that because I am not Catholic, I can't be the "Godmother", but what do you suggest in this situation?