Really? I'd have done almost anything for my son to have been able to do that much. I couldn't even get him to say Mama after 16 months(right after his father left), until he was three.
Receptive language is one of the two aspects of communication in language - the other being expressive language. Some people can speak better than they can understand or vice versa; in other words, some are better at receptive language, while others are better at expressive language. Someone who excels at one is not necessarily good at the other.
Mind you, this is the version that is used for adults. At not even two, what she has is impressive. Only an idiot of elephantine proportions(and yes, I've met some of those doctors) would not be impressed with her development.
Comprehension and follow through are two different things. Can they understand you? Most likely. Will they do it? Not always. They are still learning.
Enjoy them while they are small and cute. This phase is all too short.
Agree or disagree, as always, it's...
Just my 2cp.