Apparently, the cheque had already been cashed. Only my opinion, but I`m not sure I believe the story. People can make up all sorts of stories on the internet.
I would stop it, but I believe that in the interim the cheque has been cashed.
That is rudeness on a breath-taking scale - if that happened to me, I could be confident that I would not be worried about upsetting the couple, and that they would not be remaining within my social circle.
The lady gave a cheque because that was what the bride and groom requested.
Personally, I am old-fashioned enough to think that asking for money for personal use (as opposed to a charity donation) is vulgar and inappropriate for a wedding gift.
I bet the lady wishes she had bought them a toaster now!