It was traumatic for you, so describing it will be very hard on you. Take your time, probably several sessions, to write it down if that is what you want to do. Do you want to describe your friend to yourself? To another friend? If you want to describe your friend to another friend, think of your other friend too. There may be things you don't want to tell her, or that your friend in hospital would not want her to know.
I suggest that you start with what you feared you would see and hear before you entered the room. Go back to when you got off the elevator and are walking down the corridor toward the room. Describe what you felt, what you saw and what you heard. These are impressions, because your mind is on your friend and your feelings for your friend, not on objects. Were you with someone? Was that person guiding you? Did you feel his or her hand on your arm?
Now, go thorough the doorway into her room. Pause. Take in what you see. Do you see your friend first? Do you see other people? Or do you see equipment (the monitor, the IV, the other machines, the tubes.)? What do you hear? Beeps? Whirrs? What do you smell? Jot down what your remember first, second, third. All the detail you can remember. Maybe there are things you want to forget but can't. Don't push yourself unless you want to get down all the details.
Perhaps you locked onto your friend's face and not the monitors first. Can you describe her face? Did you notice her expression? Her eyes? Her mouth? You wrote that she was "on oxygen", so was there a canula in her nose, or one of those masks and tube arrangements that make one look like an elephant? Can you describe the colour of her skin? Blue tinged? Yellowish? Ivory? Was she wearing any makeup? How did she greet you? How did her voice sound? What did she say?
You probably took her hand. How did it feel? The IV tubing: did you notice it? You said she looked skinny and sick. Very thin, pale and weak when she squeezed your hand?
When I entered the room where my dad was dying, the first thing I remember seeing was his face on the pillow and the sounds he made. I don't recall what else or who else was in the room that moment. He was wearing one of those oxygen masks that make one look like an elephant. He was pale and he was staring at me. It's still hard for me to describe without choking back tears. I remembered the times he was so big and strong, and now I knew he was dying. It was - and is - a very pain filled memory. I've seen other old people on their death-beds; but that didn't prepare me for the reality of the moment and what I felt.
You see, a lot of your description will be affected by what you - not me or the person with you or anyone else - felt in those moments. What you feel for your friend. What changes you saw in her. What you remember about her when she was healthy.
The best way I can think of putting your memories in chronological order is to write what comes to mind, and then divide the memories on separate pages : To stand in the hallway and compose your nerves. Then walk into the room. Then walk toward her. Then take her hand. Then talk together. Then get up and say good-bye. Then walk away, out of the room. Then stand in the hallway and compose your nerves again.