Thank you to everyone for your replies
The female cat was not here over night. Only for about 3 hours. I kept her in our spare bedroom by herself. She didn't explore much. She hid in our tv unit and laid on top of my bf's playstation most of the time. I don't think she used the litter but I changed it just in case. I have cleaned off the area but will make sure to use the solution you recommended 14+.
Thank you again