If she was really unhappy she'd probably be weeing everywhere and ripping the house up. Or she'd be lethargic, lacklustre and spending all her time sleeping. I think you would know.
Is difficult turning an outdoor cat into an indoor one but not impossible as some of them really aren't keen on outdoors. Does she try to get out alot? Make sure she has lots of toys & stuff to keep her interest, Da bird is a great toy for exercise as well as a laser light, (used carefully). My indoor cats love long bits of string, boxes, feathers, playing chase or hide & seek with me and all sorts,they don't seem bored at all and never try to get out. The key is to keep changing the toys and inventing new games. Maybe she'd like a companion? (or maybe she really wouldn't!!! depends on the cat).