Hospitals often make things look far worse than what they are, they just take extreme measures for safety sake, they dint want to sued for negligence so are extra cautious.
Its a worrying time for you, I'm sure your Sis will be home again in a day or so, why not distract yourself by being positive and making her a welcome home present and you can go over the top, just to show her how much you missed her. I'm sorry if this is sounding like I'm giving advice to a child, maybe you are, maybe you are an adult, the advice is the same!!
Hope she gets well and come home very soon!!