She's gorgeous!
Out of curiosity, are her food and water dishes plastic? Our cat gets chin acne if he uses plastic bowls. We've switched everything to stainless steel and the acne went away.
No first-hand experience with amitriptyline in cats, but I've seen mixed reviews about it online. If I'm remembering right, the response to it varies from cat to cat, but if used cautiously, it may be worth a try. If it works, it seems to work well. If it were us, we'd probably have a heart-to-heart with the vet to get a list of side effects to watch for, and monitor closely.