Avoiding a defect with a cancellation Request ?

Hi all ..just after some advice please on the best way to proceed with a cancellation to avoid a defect . 

I had a buyer purchase 2 items yesterday (and looking at possibly a 3rd  today ) . Both items are yet unpaid for as she is looking at other items before paying. 

Received a message this morning asking if I would please cancel one of the purchases as she has changed her mind on that item. I am ok with doing this for her (she sounds lovely I guess just unaware  like most buyers of the new system )

I have messaged her explaining the defect system now in place for sellers and that I would get back to her later today after seeking advice on the best way to proceed from here.

Is there an option to choose buyer changed mind ? If so will I get a defect if I choose that option ?

Many Thanks, Cheers, Sheena