K.M.
I'm glad you have her in IE. As with everything, children start at all different times--normal range for walking is 9-18 months. Have they tested her hearing? A huge difference in receptive vocabulary (what they can understand) and expressive vocabulary (what they can say) is usually a red flag.
My oldest son could understand just about anything, but didn't say much. We had his hearing tested and he had 100% fluid blockage in one ear and 50% in the other. He wasn't hearing well enough to repeat the sounds. He needed tubes.
My youngest son was also speech delayed. At 18 months, his receptive vocabulary was 18 months and his expressive vocabulary was that of a 6 month old. He is now 27 months and just graduated from speech. He has well over 200 words and easily puts 3-4 word sentences together.
Yes, with some kids it just takes time. But, stay on top of it--just in case there is a real problem.