She suffered a devastating loss. Wait patiently. Tell her every 3 hours thru the door you love her and you have warm food for her. Wait patiently.
Sometimes, we just need time to grieve alone. It takes time to go through all the stages of grief. She needs space and time to get her loss.
Just say thru the door, "I'm here for you, talk to me when your ready".
I'm sorry for your sister and your loss.