How to give a collaborator write access to my blog?

I’m back to adding more to my blog, hoping it will all work. I would like to give my partner write access to my new posts. Is that what invites do? Or another way?

P.S. I have a yearly pro account if that matters to this question.

I tried the “Create Link” button on Log in — but that gives me that same link. My partner tried and it wants her to set up a new account, with no sign of access to my blog, which I want her to be able to edit.