Answer:
Ms. Gardner could make the change during the Annual Election Period (AEP) or during the MA-Enrollment Period.
Step-by-step explanation:
According to Medicare's enrollment guidelines, she could do this during the Annual Election Period (AEP) that runs from the 15th of October till the 7th of December.
Also, she could make such change during the MA Open Enrollment Period which takes place from the 1st of January till the end of March in each year.