I’ve said it before and sadly will say it again. I am totally on the side of the Casino here – they have to protect themselves.
Had your missus lost £12k on Unibet you could quite easily have said she used your card without permission and they would have been legally responsible.
to tell them you were happy for her to use the card after she has won £12k doesn’t cut the mustard – it’s called “hedging your bets”
obviously my condolences, it sure would have been a nice windfall