possible insufficient funds on customer's card

So I had a guest wanting to cancel her booking for next weekend and waive the cancellation fee. I declined the request as my cancellation policy is that to cancel without fees it must be 14 days before the arrival date. I also advise my guests at booking to take out travel insurance covering cancellation fees. 

This lady informed me she lost her job and then got quite snippy saying they'll be no money in the account when i charge it next week. 

Is there anything I can do if there are insufficient funds when I go to charge her card? or anything I can do to stop this in the future?