bi polar cause anorexia

My daughter has been diagnosed with Bi Polar.  It seems that it could alot of different things.  She is also 74 pounds at 4'11" and looks really bad, I dont know what I can do to help and wonder if it is common to have anorexia and bi polar?   She insists she is not and wont take medicine .  She is extreme in everything that she does, I know I cant change her or force her but just wondered if there things that I shouldnt say or do?

[bellagrace1969]

a very close friend of mine is extremely bi polar. she has 25 different personalities and that what they can see. there might be more but she has since developed an eating disorder. after she first developed it it was she ate like the food would disappear and since she started gaining weight she dont eat anymore and is in a hospital.