Thank you for writing in with your important question to JustAsk.
I am one to always be proactive, thus I would suggest that you first write a list of ANY purposeful utterances that your daughter says in the course of a day or two. Does she point to an object and always say the same sound, even if it is not the "proper" name (Perhaps calling a blanket a "baba" every time she sees it or wants it). Next take this list and any other observations you have made and talk with your daughter's physician. The doctor may order a hearing test to make sure that her ability to hear is not impeded (Such as with wax or fluid from ear infections, etc.).
Feel free to contact your local school district and ask for their Early Intervention Team to assess your child's current development. Usually a child has about 50 consistent utterances/words by 24 months. However, that is a ballpark range. Some children speak much earlier than others.
Lastly, consider the use of sign language in order to help promote speech. Research has proven that the use of basic sign language can help a hearing child's language development and does not slow it down. Some people do not know that sign language can be a very effective tool for the helping hearing, as well as deaf children, learn to communicate!
If you wish to have more information regarding sign language please refer to this author's website below. If you decide to start to sign with your child, keep it very rudimentary and simple. Five words at a time should be emphasized. Do not stop speaking to your daughter and try to insert signs with speech during natural situations. An example would be to sign EAT when you are asking if she wants to eat, is hungry or points to a food item.