Sure she's skinny but I am not too sure she would like the way she is bring referred to? Stating she is anorexic, unless you have anything to base this on seems quite a cruel thing to do as after all it is a medical condition, not a word to bantered about. If she read this how would it make her feel?
Re posing/lighting I personally find I normally go with it on the day, I do have a posing book with tear sheets from magazines I have collected which I use to help models of all sizes but just make them feel comfortable. Use a softer light so bone structure is not as clearly defined if you are worried about it but you may wish to clarify what kind of shots she had in mind!