a little spritz of water might encourage her to preen and mayb if u act like ur preening her, like pull ur fingers gently along a feather, shel get the idea. the first time i saw my baby

preen after i tried all of that was when i started brushin my hair in front of him...so mayb they need cues as babies before it becomes instinct....like when u wer a kid u needed ur mum to tell u hav a shower before u knew when to do it urself...
but this is just an idea not a fact, but worth a try