You are lucky to have such a lovely Aunty, and I am sure the last thing she would want is for you to be so upset. It sounds as though you are in shock, so allow yourself something sinful and comforting for once. I can only go on what you have told us, but it really does look as though the outlook is good, and she will be back with you soon. Go out and buy her a non-slip shower mat and have grab rails fitted if the doesn't have those, and enjoy her remaining years together.
Don't panic about not sleeping, it maybe that even after a warm bath and a hot milky drink that you can't, but it is not a disaster. She will probably be discharged tomorrow and you can sleep then. It is good to you have your cousin to support you, I am glad you are not alone. 