my niece's 7 month old cat is stuck in a room we can't open

my niece accidentally locked the door of the room the cat was in, it's from outside but we can't turn the key to open it. my niece's father will come by 5 or 6PM (gmt -3) to try and help up and advised us to not mess with the key because of the chance of it breaking. how bad is it? i hear cats are resilient creatures and she likes being in said room a lot but i still feel really nervous, even if my niece said this has happened before. will she be okay? we tried sliding food under the door and well try the wet treats later.