Adding Managers to a Group
1. Add the person as a regular member first. ("Manage this domain" then Groups, find the group, "Manage users in Parents," type or paste the person's email, "Add as member")
2. Click "View in Groups" service:
3. Go to "Manage:"
4. Find the user, check the box by her name, go to Actions -> Add to role -> Manager:
5. Now it shows that she IS allowed to post: