Unable To Add New User

I tried to add a new admin user a few days ago to my website at https://plantbest.com.

I forgot to check the box that didn't require her to confirm, so I tried to add her again but of course I got the error that the email is in use, and to wait a few days for it to become available again. I have tried adding her again a couple of times since then. She has checked her junk folder and is not receiving the confirmation email. I really need to be able to add her.

She is not showing up in the "Users", nor is she showing up in phpMyAdmin.

I am using wp-rocket and have tried clearing cache but that hasn't helped. I have tried the plugin "Unconfirmed" as I read in another post, but she doesn't show up as unconfirmed.

I can't find her email address anywhere on the website to delete it. I thought that it might be being held in cache, so I checked all the cache files in phpMyAdmin but no luck.

How do I delete this email address so that I can add it again properly?
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