How can I access my deceased mother's iCloud account?

See this support document: How to request access to a deceased family member’s Apple Account - Apple Support

This should help you

How to request access to a deceased family member’s Apple Account - Apple Support

Note that the type of legally-enforceable documentation Apple will require generally makes this a task most appropriately handled the Executor of your mother’s estate.

No need to duplicate what was already provided — 3-hours earlier — w/o any substantive additional info being included.