What constitutes elder abuse?

My sister concerns me with how she speaks and treats my elderly parents who are both 86. On 3 occasions in particular, she's becomes enraged, screaming and threatening them with being put in a home, and will not continue to help them. The first big blowup that I witnessed, was while my mom was very sick with that awful cough/ chest thing going around a couple of months ago. Sis wanted her to go to er, mom thought she was starting to feel better and just wanted to stay in bed for the day. My sister, the control freak started SCREAMING at her saying if she had to come drag her out she would! Then come the threats of putting her in a nursing home.))
Here I will explain a few things- my sister is a nurse!
Always critizing medical staff especially at the hospital when my parents are there for treatment. The other day she stood over a nurse kind of intimidating him while he was putting an IV in my dad
Then comments she doesn't understand why the nurse put it where he did. My parents are being admitted more frequently as they are. My fear is they will not want to treat my parents as well as they would if they (Nurses) were being treated respectfully
So as I said Dad was admitted the other day. My sister started with mis treatment of staff and was miffed because she wasn't made aware Dad has been on antibiotics. I went home to be with mom, and my sister spent the night in the hospital with dad as she always does cause she cant trust the staff.
So here is the next episode of her becoming enraged
I left hospital at 4-5am to be with mom. I knew dad was going to be fine and this was most likely a minor set back from a procedure he had done in Feb.
Get to mom and dads condo and mom still up worrying about Dad. I let her know what's going on and she goes to bed
At 700 am sister calls me on my cell and I ignore it. I knew dad was okay and they just kept as a precaution. Since I didn't answer my, cell my sister calls moms house even though she knew darn well mom hasn't got much sleep. I pick up the phone so not to wake mom. Sis wants to know the name, mg of the antibiotic I spoke of earlier. I told her, you know the hospital has all of that info, I was there with dad when he was in ER and gave that info to them. She screams at me so I hang up the phone. Now its 7:10 I hear a car door slam and I just knew it was her. I went in bathroom and locked door. I thought she would just go to where dad keeps all his pills and get the info she wanted. BUT NO, she wakes up my 86 yr old mom who has gotten maybe 2- hrs of sleep. See when my sister is angry she'll take everyone around her down with her. Mom wasn't responding well cause she was so exhausted and didn't have her hearing aids in so sis decides to startle her by saying she needs dads living will and power of attorney NOW. She Scared my mother. And of course now mom is responding. I really feel these behaviors are abusive . I'm afraid that one day she may physically harm them when she becomes enraged like this.
The third incident occurred the other day while my dad was still in the hospital. She decided that was a good time to have what was described to me as a big blow out!
Sorry this was so lengthy but I thought I needed to explain so you could understand. I appreciate feedback. I would like some opinions on weather this is considered elder abuse. Btw.....mom and dad are all there, mom still cooks, wears makeup, and dad still drives and does things around the house