Yes, cats are very capable of reading human moods, especially the moods of humans they live with. We have no definitive answer as to why this is so. Do cats recognize human emotions because they share emotions similar to ours? Are they simply reacting to sensory cues? Or both? I believe that cats, like many other animals, are naturally empathetic, and in this case, your cat knew that you needed comfort and did her best to provide it. Your anxiety may also have transferred itself to her, so perhaps she was looking for a bit of reassurance as well.