How to edit a site with its own domain?

I’m editing a friend’s WordPress site and she has her own domain. It looks like she started a website with the WordPress domain, didn’t change anything from the template, and then changed to her own domain and that is the site that’s active.

The only way I can even tell her active site exists is because I went to the W logo on the top left and it’s listed as a site. But it won’t let me log into that site to do anything to it.