She had to have obtained your password in some way. I just tried this with my mother. I've never been signed in on her computer and I sent her a transaction link. She got the Uh-oh wench and a message that said:
You are trying to view a receipt that does not belong to you.
Go back to Etsy.com
I also tried it on my computer. I copied a transaction link in Firefox, opened Google chrome and pasted it in. I got prompted to open an account with Etsy. (My mother probably had her browser set to auto sign in to her Etsy account because she saw the uh-oh wench and I didn't.)
Have you ever been signed in on her computer?