How long after Anne Frank death did the British liberate rescue and free Bergen Belsen?

On August 4, 1944 Achterhuis was invaded by the German Security Police because of an anonymous tip off. The Franks, van Pelses, and Pfeffer were taken to the Gestapo headquarters to be interrogated overnight. The next day they were moved to a prison, and two days later, to Westerbork.

On September 3, they were moved to the Auschwitz camp, where the men were separated from the women and children. There, children under the age of fifteen were sent to gas chambers, but Anne had turned fifteen about three month earlier. She reasoned that her father had been gassed upon arrival, but he hadn't.

On October 28, groups of women, including Anne, Margot, and Aguste van Pels were moved to Bergen-Belsen. Edith stayed behind and died of starvation.

A typhus epidemic spread through the Belsen in early in 1945. Margot became extremely ill and soon became so weak that she was not even able to leave her bunk. She fell from her bed and died from the shock. Anne perished a few days later, only a few weeks before her camp was liberated on April 15, 1945.

So, Anne lived in the concentration camps from September 3, 1944 to her death at age fifteen in early March, 1945.