I’m sorry for your situation. My only advice is not to leave anything unsaid, tell her how you feel, thank her for what’s she’s done and she’ll understand.
My Dad died relatively unexpectedly just over 2 years ago, due to COVID I wasn’t allowed in to see him for the 6 weeks he was in hospital. The exception being why he was in the ITU but he was sedated so wasn’t able to talk back. I tried my best to say good bye and tell him how I felt but he was pretty young (65) and we all expected him to pull through. He came out of the ITU and I wasn’t able to see him again, e also couldn’t talk on the phone so I never got to properly speak to him. It is the biggest regret of my life.
Just tell her how you feel but don’t beat yourself up, you have been there with her and she will appreciate that