Order delivered but buyer says it never arrived. Can they claim aTOz?

Hi all, So Amazon is always a little tricky when it comes to buyers. A buyer has come back 6 weeks after I shipped an item stating it never arrived and is demanding a refund. The item was tracked and delivered 12th November. Whats the story here if she goes aTOz claim? Any time Ive challenged an aTOz Ive always lost even though Im fully sure Im in the right? Amazon Customer SUpport are usually a waste of time so thought this place might be good for advice.

Am I better off just refunding her?

ANy help is appreciated