You need add user to taskspace application role. Login as ts_designer, go to configuration->roles, add user to proper roles.
ts_designer is the one we included. Rest, depends on your application and usage.
No. Ts_designer role is for developers to allow them to make updates to application.
Authentication is different from role assignment. Yes, you need to add her to one of your taskspace application role. Roles are different from groups (group is typically used for security and role is used for functionality/UI).
Your taskspace application should have its own custom roles (best practices). In Taskspace Designer, you can see which roles are used/configured for your app.