I think you'll have a very hard time turning under the edges of a flannel snowflake made from a pattern that was intended for wool (meaning no seam allowances added). There are just too many ins and outs and sharp angles. Raw edge appliqué is probably your best bet, but fusible web is not reliable on either wool or flannel due to the nap. I wish you luck with whatever route you take.
As an aside, Wonder Under can be run through an ink jet printer so patterns can be printed directly on it assuring an exact duplication of the pattern and no wasted time tracing.