School councillor trust situation

You are the school councillor at an all girls school. Two weeks ago, one of the older students, Katie, comes to you and tells you that her best friend, Anna, just told her that she is depressed and has been self-harming for the past month. Anna also told Katie that she is the only one who she has told, and that she doesn't want Katie to tell anyone. Katie is feeling over whelmed and scared for her best friend and has no idea how to deal with it. Katie doesn't want you to talk to Anna, because then Anna would know that she betrayed her trust, however, she also doesn't want to do nothing. You suggested to Katie to try talk with Anna about talking with you, as you can possibly help Anna get through this tough time.
Today, Katie came to you in tears saying that Anna cut herself deeper than ever before and is now really worried, but still does not want you to approach Anna in the case that she gets angry at Katie and betrayed by the one person she can trust.