It *might* be a learning disability, but that should be answered by a specialist. How is her mood? (Stress/depression may cause difficulty to concentrate.)
It may not be a lack of ability to follow instructions, but a learned behaviour. A possible explanation is that your DD may have learnt to "space out" (think of something else) all the time while she is at school, to cope with extreme boredom, when everything around is very S-L-O-W and meaningless. (Disclaimer: I am not a specialist, and this is just one of the many possibilities.)
Do you see the same behaviour when she does something which she is very interested in?
