It looks as if settings has changed the account to mine instead of my wife's. The account is greyed in settings so that I can't change it.

There is an option to delete the account but it says that will remove everything. On iCloud. I've put a test entry in calendar on iPhone and it appears on iPad. I've then deleted it from iPad and it's gone from iPad so iCloud seems to be working but in Safari all my bookmarked tabs on iCloud have gone.