This might not be much help, but...
My mother also writes songs but has no musical training. Somehow, she connected with a retired professor of music theory from a local Bible college. He's transcribed most of her songs. Then they have an incredibly talented young person in their church who has taken many of these and transcribed them into orchestra and choral works.
These avenues might not be open to your sister, but I just wanted to point out that she should be open to the most unlikely circumstances. If these songs are from God, she needs to trust him to find a way and look for his leading.
