Hey, @j24633,
Your question is a little confusing, but let me try and help you through a couple of options.
It sounds like the user has a new email address... as opposed to just moving to a new department with the same address. In that case, her new email address is already set up in her new department, and they should provision her with a new Zoom User add-on. To be honest, this probably isn't ideal, as it means that all of her meetings, Personal Meeting ID, any Chats, and any Contacts set up will be lost and need to be recreated; much better to have more centralized Zoom account management that can simply move her into a new department -- all under the same account structure. But that's not your problem. 😎
This Zoom Support article will probably be helpful (or maybe overkill/TMI, but worth reading). Basically you can delete her old email address from your account, and any add-ons that were attached to her account then should become "unattached to anyone" on your account. Assuming you hire a replacement, when that person's email address is added to your account, you'll need to re-assign the available account add-ons to her email address/user account.
I hope that's helpful! If you need more info, reply to this thread and I'll try to help more if I can.