My DS2 also wasn't premmie but he did have some speech issues. He had about the same amount of words as your DD at the age of 2, actually maybe even less.
He is now almost 3 and he is a real chatterbox. He is still somewhat behind in his speech but it isn't of concern to the ECHN or Dr as he can say & repeat words asked of him, he is just not a big talker as yet. He also fills in the missing words in a sentence with a hum which is apparently a good thing as he recognises he needs a word there but just doesn't know what the word is... hopefully soon enough he will know most of the words. We're still waiting to get him in to see the speech therapist though so I will see what happens from there.