Angel,
Just by starting this thread you have helped your sister. It is obvious that you care about her and want to help.
If Liza tells you that she is being annoyed by your efforts - you just tell her to get on in her and we will woop her for you - JUST KIDDING.
Sometimes the best way to help is just to let her know you are willing to do ANYTHING she wants done from holding her hand to washing her floors
. However, for specifics - does she have her own home? If she does, you can make sure she has plenty of easy to prepare foods. I always made sure I had disposable dishes & flatware so I didn't have to worry about dishes. Make sure she has a recliner set up near the bathroom so, if she is tired, she doesn't have to worry about too much effort.
Have a table or small cabinet near the recliner for meds and magazines, etc. Have a supply of small bottles of water nearby - they are easy to pick up and are disposable. Also make sure there is a fairly large trash can within throwing reach. Telephone should be on that table/cabinet also.
While she is still in the hospital, stop by and see her but be happy just to sit quietly and hold her hand. Talking can be an effort the first day or so. She will be using all her energy to overcome the trauma of surgery so don't expect conversations. I was happy just to have someone in the room that I knew was watching over me.
Enough for now. Let me know of any questions from here.
Your sister is very lucky to have you.