What would you guys do?

I shipped a bundle to this buyer and they say they didn’t get the package and others and said it was shipped to their work?? USPS says it was dropped off at a mailbox and I’m not sure what to do/ not sure if she may be lying? I’m trying to give her the benefit of the doubt, but I just don’t know and I don’t wanna give her a refund if she’s actually lying??