I had a very similar problem with my clown. She refused to eat pellets, flakes, or frozen mysis when she was in quarantine. I was very afraid she'd starve to death. I got some good advice tho and started feeding her live
brine shrimp. She went after those quite enthusiastically and when I transferred her to the display tank she finally learned to eat the rest of the foods I offered after watching the other fish. She still is picky however...she much prefers the live food and frozen mysis mix over the pellets and flakes...
in short, try live brine shrimp.