Does she have older siblings?
Sometimes an older brother will frequently speak for his younger sister and cause you to imagine that there is a delay when there isn't. This can also mask a delay that is actually there. Regularly speak with your toddler privately to make sure she's capable of communicating on her own.
Is your child a twin or other multiple?
Twins and multiples sometimes develop special ways of communicating with each other. They can also tend to develop speech and communication skills at a different rate than other children. Sometimes this is a concern and other times it is not. The best way to know the difference is to educate yourself about the speech development issues unique to multiples.
Are there two or more languages spoken at home or school?
If your child is regularly exposed to more than one language (sign language or spoken languages), then she may be slower to speak. This is not generally a sign of a true developmental delay. Just think of it as your child doing twice the amount of language processing and you can see why it takes longer for communication to develop. Raising multilingual children has many benefits, so don't avoid speaking more than one language just so your toddler will speak more or sooner.
Does she stutter?
Most stuttering develops in children during the toddler years and it's a perfectly normal part of language development. Be concerned if it hasn't disappeared about 6 months after it starts or if the stuttering is accompanied by exaggerated facial expressions.
Language delays can be caused by many different factors (like hearing issues or muscle problems) or could be part of other conditions such as a learning disability or autism. In any case, prompt evaluation, diagnosis and treatment are the keys to the best outcome for your toddler.