My boy is an indoor only puss due to being FIV+, and he's absolutely fine with it, happy, healthy, and above all.....safe
As others have said already, you need to make sure that there is loads to stimulate her, lots of toys, lots of interaction with you, and yes, you've guessed it, an activity centre would be great lol! Also, you could give consideration to getting her a friend for company, kittens are usually ok with accepting newcomers, so they could grow up together.