Anne's reflection of her state of being in this statement is probably one of the most profound elements present in the diary. She expresses happiness and thankfulness for being able to be with her family, and for being alive, when so many others are not. Each time Anne and her family receive news from the outside world about what is happening, what they hear makes them thankful for being alive. When they hear about families being separated (a fate that will fall upon their own family at the diary's conclusion), Anne feels elated and thankful for being alive and being with her family. However, this condition of gratitude collides with its countervailing force of despair and overwhelming sadness because this is her life. She must profess thankfulness for simply being alive. Through no fault of her own, Anne experiences great despair because the condition of her life is so terrible and horrific that excitement must be present at the mere prospect of life.
It makes sense that Anne, an adolescent struggling to make sense of the world and a particular setting where little sense can be made, would vassilate between happiness and despair. We see adolescents experience vast emotions in settings that are not even slight compatible to Anne's predicament, so it would make sense that Anne's experiences and physical and emotional atmospheres would change from great happiness to great despair. Her reactions are only reflective of a setting in history where the emotional frame of mind of every individual who had to endure it could only be described as "challenging."