Issue with sharing Library and Brand

Hello, I have created links and invited them by email to share our library and brand to a fellow colleague. I did see that they requested access to join but when I click "accept" it's not allowing me to add them and gives me the following message. I and a couple team members have an adobe for enterprise account while the person I'm trying to share it with isn't included in our plan (doesn't have access to all the adobe apps we do) and is currently using the free version and will be signing up for the premium version. Does she need to be added to our enterprise team or is the issue something else? Thanks.