My sister is in stage 4 dementia and won't let anyone touch her. She will scream and say she is scared making it hard for me to change her.

Your sister needs to be in a memory care facility now. Get her placed.
In the meantime she also needs to be medicated. Whatever she's on isn't working. Call her doctor and ask him to prescribe lorazepam or diazepam in liquid form. About 15 minutes before you and an aide (two people) are going to be getting her washed up and changed, give her something tasty to drink and dose it. This will keep her mellow enough to get her washed up in bed and in a clean diaper. Dose her at night too. Ask the doctor if he can prescribe a sleeping medication that would be compatible with a benzodiazepine drugs. This will help put her out at night.

I was a homecare worker for 25 years. I've seen this scenario play out many, many times. A person has dementia and won't allow themselves to be cleaned up or changed. You do it anyway. Let her scream herself voiceless, do it anyway. A person cannot be left in a spoiled pull-up or diaper because that will lead to so many types of health problems from UTI's to skin sores. Your sister is at the point now in her dementia where pull-ups should be a thing of the past. She should be in actual tabbed adult diapers now.

Look for a memory care facility. If she gets too hard to handle you can bring her to a hospital ER and ask for a 'Social Admit' because she cannot be cared for at home anymore. They will admit her until they find a memory care that has an available bed. This action is the last resort.

Advice is given to get an aide or place someone in a facility. This is not as easy as it may sound. Aides are hard to find, sometimes unreliable and expensive. So is memory care. You can't put someone in a care facility unless there is a space available. Just because a person needs to be in such a facility it may not be possible to find one. Leaving a person at the hospital won't work, because as soon as they can, the hospital will want to discharge the person. They will find a place for her, but probably not where you would wat her to be.

Cost is another factor. Your sisters will have to spend all her money (if she has any) before she will be eligible for Medicaid.

You are lucky to be her sister rather than her spouse. Spouses lose most of the money they have managed to save throughout life when one of them has to go into a facility. Half of all the assets (minus the house and one car) must be spent before the person in the nursing home qualifies for Medicaid. It may not make the spouse still at home into a pauper, but it comes darn close.

Thanks for all the advice, I feel better when someone actually listens. She is on medication but it’s not working, I don’t want her to sleep all day then she will be up all night. I have been through 3aides they are not much help, but they do sit with her. It’s so sad and heartbreaking

She requires a care team now, and likely medication as well. She is no longer appropriate for in home care. Not everything can be fixed. She should be taken to an ER for evaluation and for checking for a UTI. If you must call 911 to accomplish this, then do so. As soon as she is in the care of the hospital, leave; they have your phone number. And get social services working on placing her; let them know you can no longer physically manage her care.

Your sister obviously needs some calming medication(s) prescribed by her neurologist, so please make sure that happens.
She also may be having some pain as well, so that needs to be addressed too.
If her aide cannot get your sister to cooperate, you may have to find another one that is used to dealing with folks with dementia, as not all are.
And honestly if your sisters care is just too much for you all, then placement in a memory care facility will have to be the next step.

She needs to go into memory care. They will give her medication to calm her down.