Once you know something is changing, the question shifts from whether to act to how to help without taking over.
That balance is the whole job, and it moves over time.
Structure does more work than reminders.
Predictable days are easier than varied ones. Things kept in one visible place are easier than things put away tidily. A large clock showing the date, a written plan for the day, and keys on a hook by the door remove a dozen small failures without anyone having to be corrected.
Change one thing at a time and give it a fortnight. Rearranging someone's home in a weekend is disorientating, however well intended.
Support is easier when you know what you are supporting.
Read caring for a loved one for what to put in place early, or resources for caregivers for organisations that can help. A repeated baseline tells you whether things are stable or moving, which is hard to judge from day to day.