Thank you, Rebaquilts! That's a great explanation.
I thought I might take the easy way out and order some small pieces of novelty fabrics from Etsy for fabric C. They have quite a few entries for 9" x 11" pieces. It would be easy to cut them to size.
I noticed that she says fabric E could be the same as fabric B; I have a 2 yd. piece of fabric rejected for a border, so I was thinking I might use that for both.