I'm not a teacher, but I've had this problem. If I violate some unspoken code amongst piano teachers with my suggestion, don't hurt me!
I think your idea will work-If self esteem is what she needs, this would probably be an opportunity to give her that feeling of accomplishment.
Also, has the student ever played Knecht Ruprecht by Schumann? When I finally learned to play softly, I somehow forgot how to play loudly. My teacher prescribed me that piece, and she made me play the ƒ parts ƒƒ. I soon remembered how to play loudly.