What are two ways that Ilse saved Gerda's life?

In the memoir, All but My Life, the friendship between Ilse and Gerda is what keeps Gerda alive. Ilse saves Gerda's life in a variety of ways... she gives up her food on a number of occasions, so that Gerda can keep up her strength. She also takes on extra work for Gerda when the two are assigned to their work details. This included assisting Gerda and even volunteering to do the work for her.