Katy, I am only guessing what your frame will look like. Would two pieces of flat dowel do the job, one for the top and another for the bottom?

If you are using beading wire, you could leave a few cm of wire at the top and after attaching it to the wood, thread a few beads on it and twist them into a flower. At the bottom you could do the same, or use the longer end of wire to create a tassel. ?:|

Then you can attach the top and bottom dowel to the frame, either nail it or glue it on. I also like the idea of using pretty lace.

Just my opinion. I love beading and the idea of a beaded window sounds great.

Erica 😄