In Gyanamata’s book (God Alone) page 36, it says that Divine Mother would never let Yogananda be in the room when one of the devotees passed away. Why was that?
And in page 37, "You must know that Gyanamata’s passing symbolizes that I will be leaving this world shortly." Why that?
One cannot know for sure the answers to your questions, so my answers are only speculations.
To answer your first question: Divine Mother would never let Yogananda be in the room when one of the devotees passed away, perhaps because She didn’t want him to try to prevent that person from passing, and keep the person in the body any longer.
To answer your second question: It might be that Yogananda’s last task on earth was to free Sister Gyanamata, and after she was liberated, his work was done, and it was a sign that he too could leave the body.
I hope this is helpful,