Thanks for your replies!
MIL kept saying they said they had put a hold on her credit card which I couldn't understand.
None of the $1500 were any onboard purchases. The weird thing is that the amounts were like $212.84, $415.73 & then $818.54.
It would not have been a problem if they took these amounts from the total charge for the cruise but they have been charged in addition. She is annoyed because she still has 3 weeks left of her holiday and is now down $1500 until they see fit to refund her money.
This just seems crazy to me. When we went to a Club Med resort they did a pre-authorization on our credit card to make sure we had enough available for any purchases but the money did not actually come off our account and we had to sign the credit slip. She did not sign any credit slips for this money - they just took it!
I think she will definitely take the matter further as it seems very bad business practice.
Thanks again for your replies.