I hope it's okay that I share this with you...I have been a medium since I was a child - communicating with spirits. For many years, I did professional readings, including on BBC for 5 years, and also on stages, connecting audience members with loved ones in spirit.
I can promise you - from hearing this many times from spirits over 50 years - the soul chooses who will be present - or not - when it leaves the body. Given the way your grandmother lived her life, it makes so much sense that she would have chosen to go when she was alone. She was fiercely independent, didn't want anyone to have to take care of her - and given that she had no choice about that at the end of her life, it would make sense that she would choose to leave her earthly life by herself.
She hears you when you think or speak about her and she's always near.
Really hoping this is not upsetting. I'm so sorry for your loss. Your grandmother sounds like an amazing woman.