Poor little thing - I hope she's been doing well since. Like someone else mentioned, language, like other skill areas, can develop at such different paces. It's always good to monitor and make sure there is ongoing progress. My daughter used a lot of sign language. We started around 6-9 months I'd say and she was not very verbal probably until about 2. Once she started talking, she talked in sentences and now doesn't stop. My son pretty much skipped over the signs - learns them after learning new words. At just 2, there's really nothing he doesn't say.
Before becoming a mom, I was an early childhood teacher. The best way for little ones to learn language is to hear LOTS AND LOTS of it in all different forms. Sing plenty of songs and poems, read books - any kind about any topic. Talk about what you are doing - describe the steps in diferent activities like cooking or cleaning. Start conversations with her and model verbalization for her when she gives any nonverbal clues - "Oh, you'd like your milk now." Label items you see - when going through the grocery store, talk about all the things you are putting the cart and what you might make with them.