There are lots of activities fortunately. It may be limited by what she's actually interested in, of course. There are the evening Broadway style shows. The different lounges host various performers as well. There will be things like cooking demos, beverage tastings (extra $), craft classes, trivia, BINGO, game shows, learn to draw classes. The spa and salon offer various services for an additional fee - maybe she would enjoy a little pampering. If she has a balcony room, you can't disregard the magic of ordering some snacks from room service and enjoying the views from the balcony with a good book/knitting/just sitting and enjoying. She can also enjoy a sit-down breakfast and lunch in one of the main dining rooms (varies by ship which one is open) if she'd rather do that than fight the masses at the buffet.
Every cruise is different, but there will be an array of activities offered daily and listed in the Navigator, which you can access once on board either through the app or I believe you can still request a paper copy.