Thank you for the provided URL.
The "Sign in" link is displayed on this page, because there is no Single Sign On feature on this page.
As far as I understand, you have created a separate http://thesewingspace.com/zip-sale/
page and added Ecwid integration code manually to it, while the store itself (http://thesewingspace.com/store
) has been created with the help of Ecwid plugin
, built into Wordpress. When you have enabled Single Sign On feature, it has been applied to Ecwid plugin only, not for the pages you have added Ecwid code manually to.
I presume you would like to place the link to http://thesewingspace.com/zip-sale/
page somewhere in the site menu, correct? If so, you don't need a separate page for this category. You just need to add a link to this category, located inside your store, but not as a separate page. In this case the category will belong to Ecwid plugin and will inherit all the settings you have for this plugin, including Single Sign On feature.