Will we lose our deposit?

Hello! Our lease is up at the end of this month and I'd like to find out how much we would lose from our deposit for having a cat when our lease clearly states "no pets allowed." Our landlord showed the apt today for new tenants and noticed our cat. We've hidden her for the last year whenever the landlord or the super come. She didn't give us a warning or anything. Is she just keeping quiet until our lease is up and use that information against us by keeping our deposit? If so, how much could we expect to lose from our deposit? Does anyone have any advice regarding a similar situation? I'd appreciate any insight! thanks!!