Help! My Goffin's atoo is clipping her feathers.?

My family and I don't know what to do. Nothing has changed around our house and we dedicate most of our time to her. Whether I'm doing my homework or watching TV she is usually on my lap or playing with blocks outside near me. Every day for at least an hour, I give all my attention on her and play games with her like peek-a-boo or chase. Sometimes though while she's playing she will just ditch her toy and start clipping her feathers or hide under the table where I can't reach her and clip them there. She doesn't seem depressed because she is always hopping around the living room yelling out the only word she knows while flapping her wings around playfully. We asked an avian expert what to do and she said to fix her diet. We bought the (expensive) food she recommended and we saw no change. Her vet said she was very healthy so it's not that she's sick. Please help, I'll love my birdie no matter what, but I feel kind of bummed when i pet her & don't feel the same fluffy feathers I used to