From a teacher stand point, you may be dealing with something called 'dysnomia'. Then again, you may have a little Einstein on your hands - he didn't talk till he was 3.
My children (both boys) were lagging in vocabulary - my 4 year old didn't start using what I consider real sentences until about 2 months before his 4th birthday. Three months after he started, he won't stop talking - about the moon and it's phases, the difference in insects and spiders, what makes a car go, different kinds of trucks - the boy is insatiable. My 19 month old is not as far behind by the charts - he's 13 months solid talking, but he has a preschooler's vocabulary in sign.
I recommend that the two of you get some basic sign language going - it lets her communicate in words with you (thereby setting up a formal language structure, instead of pointing or pulling) without having to think of the word. If dysnomia is an issue at all, the sign language will help her brain form pathways another way. Once she signs, you can work on talking while signing, then eliminating the signing.
Another thing you can use is file folder games - I love them so much more than flashcards, for everything. Google the term if you haven't heard of them - you would want games that deal with associated words, colors, matching - see if you can get her to say (or sign) the word for what she's looking for.