I like a lot of the ideas above. Also, since she loves theater, look on Playbill's website for theater-related gifts
http://www.playbillstore.com/ . If she likes to sings songs from shows, and can read music, you could get her the songbook for one of her favorite shows. Etsy also has a lot of theater-related gifts - if you put in the name of a show she likes, you might find a lot of gifts there (if she likes Les Miserables, for example, there's everything from jewelry with Les Miz logos and quotes, to handmade dolls of the characters, to clothing with lyrics from the show).