Like many people associated with the Imperial Family, Anya Vyrubova was a complex person. I know she expressed different views in her later memoirs, but at the time of her first memoirs, there were few people who could contradict her, so she was free to construct her story the way she wanted to. Why would she lie? Those who knew differently were dead! What she gained is she was able to tell her story her way, she was able to make herself look far better than she really was. Can you trust anything she wrote? Well, you know she was a liar, so I would say, just like the Bolsheviks who had no problem lying, you can believe what she said that can be corroborated by another source. Otherwise, it's a possibility.