User unable to view shared calendar on Google Education

[MarcLister]

We have a shared calendar for our school of all the upcoming events. Each Friday one of my colleagues will send out a link to the next week's calendar entry for staff to see what events are happening the following week.

 

The link is sent to the whole staff group which is [email protected]. One of my colleagues can't access the shared calendar despite me sending her the link that adds the calendar to her Google Calendar twice. No-one else has had the same problem. My colleague is a member of the staff group. Any ideas what is wrong and how to fix the issue?