Thinking outside the box .... how about a large image, like the quilting is the stained glass design. Heavy black thread.
To me, when I think stained glass I think Christian church so I'll list those suggestions first
Large cross with ray's coming out diagonally
Praying hands ... again with diagonal rays
Jesus praying ... again with diagonal rays to the edges
Non denominational designs
Butterfly
Vase of flowers
large tree