You need the wisdom of Solomon to make the right choice here. Many will defend house cats as being happy but personally I feel sorry for them although I do understand. I have tried to keep cats indoors in the past after losing a much loved pet to the road but if you've ever had a cat that is free to go out you will know how much pleasure it gives them, lying in the sun, scrambling up trees, eating grass and chucking it up when they come back inside, exploring etc. you need to think how much you want to keep her, will you want her staying indoors for many years? At 8 months she's young enough to happily re-home. Don't worry about the sleeping though, they average 18 hours sleep a day as an adult, more so at her age.