My friend makes herself throw up to stay thin. Is that bulimia?

Whether or not your friend meets clinical criteria for a diagnostic label doesn't really matter. Making yourself throw up to be thin is unhealthy and disordered. It can cause big problems if she does not stop. The worst is a condition where she loses control, called Bulimia Nervosa, where all types of serious problems occur, even death. Your friend is playing with fire, lighting the fuse to a bomb that can ruin her life. It will get worse if she doesn't stop. It will not stay as it is.

I hope your friend is mature enough to realize that she does not know enough about this. She needs to be listening to therapists who specialize in eating disorders and believing them, rather than other bulimics who have the disorder.

Show her my answer to your question and encourage her to talk to a counselor.