Does my wife Kathy have her own iCloud account? How does Kathy check her activity? How does Kathy log into iCloud? Thanks Paul O

If she has her own unique AppleID, she uses that to access her iCloud account. If she’s using your AppleID, then you both are accessing the same account.

Each AppleID used to login defines the account used for Apple services (iCloud, iMessage, FaceTime, the App, Music and Book Store,...). So to have separate accounts for anything, each person must have and use only their own unique AppleID.