@Adalira:
I suggest the same thing Pearlie says, just refund her, BUT I also suggest commenting on the post she made on her page. Something along the lines of " Hello, I'm sorry you feel that way. I've sent you messages at both your etsy, email, and here on facebook and have yet to recieve a reply. Please message me on any of those platforms and we can get something sorted out. Thank you." Make sure you don't let your emotions get in the way when you comment/reply to her. (think retail worker who has a smile on their face all the time. That has to be you now.) I also think that if she replies to you, gently mention that you do not sell harry potter wands and that your wands are not intended for small children and shouldn't be given/bought for them as gifts.
And Like Pearlie says, just a thicker skin is basically the only thing you can do to make this hurt less. I haven't gotten a bad review yet, but I know that won't last forever haha.
Also, I think you should keep the review section of your page up :) It's a good tool to use where all of your happy customers can leave their praise. One bad review won't kill your image, mostly if it's the only review, it'll make happy customers visiting the page see they can leave a review and notice that you've got a bad one and write even more praise in their review for you.