I agree that Amy Grace is a lot like Amazing Grace, but I still think it's sweet! As you said it's not as if it will be called by all names on a daily basis (except when she's in trouble of course! )
Here are few options I thought up anyways -

Amy Bree
Amy Kate (or Caitlin)
Amy Leigh
Amy Pearl

I'm not much of a fan of Amy Patricia Frances.
I wish you all the best!