Hi Carlen Bowie,
Thanks for sharing your experience with us.
We understand you want to share SharePoint site with an external user, after you share the site with the user, she cannot access the site.
We would like to suggest you firstly check if you have enabled
External sharing globally for SharePoint Online(tenant level) and individual site collection level.
At tenant level: SharePoint admin center>sharing>Sharing outside your organization.
At site collection level: SharePoint admin center>Site collections>select a site collection>Sharing>Sharing outside your company.
You can refer to the information in the following articles:
Share your Office 365 sites with external users
Turn
external sharing on or off for SharePoint Online
If the external users still cannot access your SharePoint site, we'd like to confirm the following information for troubleshooting:
1.You mentioned "The user in question was having trouble accessing our sharepoint site".
When the external tries to access the site, does she get any error message? If yes, please also share a related screenshot.
2.A screenshot of the error message when you share the site with the external user.
3.Does the issue happen to the specific external user?
4.What is the permission level when you share the site?
Regards,
Tina