Prayer quilts are my favorites.
A few ideas to share with you:
If she is a music minister, there are lots of lovely fabrics with hymn lyrics, like Amazing Grace, etc.
There are so many lovely patterns that incorporate Crosses, too.
If you have an embroidery machine, the possibilities are endless.
A tied quilt is a wonderful idea as well.
You might want to put a panel on the back so that individuals from family, friends and church can sign it and pray for her. I can't find the thread right now, but I did one for a man who comes to the dog park we visit. That way she can read the prayers, thoughts and sentiments.
Also if you do a search of the board, you'll find lots of wonderful ideas.
Wishing you many blessings as you embark on this project - and prayers for your friend.