That's what I'd say, too-- we also have a perfectionist who loathes practicing. It's always a work in progress, and yes, it also is a matter of nagging on some level, but it's too important for her to have a few things where effort is
more or less proportional to results, and she is not "perfect."
Yes, initially your efforts to get a handle on perfectionism WILL increase your child's anxiety and stress. Think of it as a necessary, but unpleasant intervention like a vaccination or blood draw. Some things aren't negotiable because I'm Mom and I
do have my child's best interests in mind-- longer term than she does, in a lot of cases. SHE is about whatever gets her what she wants (or wants out of) in the moment or immediate future.
By the way-- I meant to say this earlier:
Even if you now have a "label" to go with your child's ability and potential, do remember that you still have the same child that you've been parenting all along. She's the same child. You just have more information. 
