Friend....I don't know much about cats but I think she is having any kind of problem on her head or other problem something like that..... and if you cat is missing that means she is warning you to get back maybe she is having any kind of problem...... maybe she is in pain or a kind of an suitable condition that's why she is hissing... it can be hyperthyroidism.... or nervous system disorders.. which led to a certain hissing...