Gosh ,and I also see that your customer already got a positive from you, right off the bat.
She was new to Etsy also, so for her, she seems not to understand how important this is for you,in terms of reputation.
You sound like such a very nice person too. Sorry this had to happen. Sounds like you need a hug!
(BTW, I really like your egss and other items & your photos are amazing...such a sweet shop and ready for Easter too!).
First.... stay calm.
Come off as sweet as you did with us.
Take a deep breath and do a KISS and MAKE UP via ETSY.
Second, since you have her home address, send her a sweet card (a very nice one) explaining "by hand", that you'd be willing to re-do the order IMMEDIATELY etc. In fact, tell her you are working on her "Re-do" eggs today.
Rub it in, so that she understands what great customer service you do for your customers.
Come off just as sweet as you are, because well...you are sweet,right?!!....
Third, in your nice card, ask her to re-consider to do the KISS & MAKE UP, to reverse that Negative.
Shoot for a Reversal...Not a Neutral but a complete Reversal,especially since it will cost you $$ to redo the entire order,plus, you will have to ship it to her at your cost...ugh!...
Reason I say this is because you have plenty of time to re-do her eggs and get that Negative reversed..... BEFORE Easter!
Your aim is to get some Easter-time sales.
Send her your sweet note, tomorrow.
Begin doing her "re-do" eggs for her, tomorrow.
Ship them to her ,if you have to, and make her feel completely guilty for not having even given you a chance to re-do her eggs, before giving you that NEG so fast.
I think that after she gets your "re-do" eggs, she will feel like she had been unfair with you. Let her mull it over.
Lastly, after all this is done & that Neg is gone, log this experience into your brain's permanent memory, and learn from this. Use this experience.
Yup... use this as a learning experience, and vow to just always stay as sweet as you are, and to continue to do great work on your items & Shop.
Good luck....
L2