We only send a maximum of 1 email per week to your CrewMates (for good reason).
In that email, your CrewMate has the ability to click "Authenticate All" if there are multiple entries requiring to be authenticated.
Please check your CrewMates email address, you won't believe the number of fat fingered emails we get - there is now such domain as gamil.com
Please ask your friend to check their junk mail box.
Ultimately it is best if your CrewMate is a NauticEd student as well. In that manner their logbook is automatically built and the entries are easier to track. Please MAKE SURE you use the same email address for them as a CrewMate as for them as a student.