Wisdom to know when a person can stay by themselves for 4 to 6 hours?

Your friend can fall at any time, even with you or other help there. In fact, it’s likely and more likely as time goes on. Being with her all the time is giving her the illusion that she’s living independently when that’s not true at all. You can’t plan for every possibility and you can’t help someone who doesn’t want help. Back off your time with her. It’s the only way she’ll see her need to make changes and get further help

The fact that you are questioning this means that you really do not think she she should be alone.
This is called " Listening to your gut"
Listen to it because gut instincts are usually right.
She has dementia, she can not make rational or safe decisions.
She accepts you and another person to help her. I am thinking that she gets upset with someone else because she does not know them and if a person is in early or moderate stage of dementia she may still be trying to hide that fact and it can be exhausting to do so. The person that takes over for you and her other friend should have another caregiver come in while you are there so she gets used to this new person. Once she is comfortable with her "new friend" she might be less resistant to allowing this "new friend" provide care. In order for her to get comfortable you should run an errand leaving the other to take over for a bit until you get back. Do that increasing the length of time you are gone.

What exactly does "I am a live in friend and care giver mean"? Are you paid? Are you a roommate? Is there a lease or contract in place?

If she's yelling at you, you shouldn't tolerate that ever, even if you have a lease or contract. Yelling is not acceptable. You have a life, and you are entitled to live it.

She says she can be by herself and so I don't understand why you shouldn't take her at her word. You are not responsible for 24/7 care, which is impossible.

Your friend sounds unstable and your living situation sounds precarious, and could turn bad at any moment. I would start looking to move out and find your own space. Rent a room with a bathroom. Since the pandemic started, people who used to make money renting out rooms are desperate.

I think you should start planning for your own future. If she were to fall, and could not return home, what's going to happen to you?

As a live in do you mean you spend the night getting her ready in the morning and then someone comes in the afternoon. When do you return? When is she alone 8 hours?

You could try an Alert pendant. If she falls the motion of the pendent hitting the floor will alert the operator connected to the device.

But I think that is the least of your problems. Your friend suffers from a Dementia. I bet you are finding you can't reason with her. Short-term is being effected plus being able to process what is being said. Her fall may have escalated her Dementia. So what I see is her Dementia being why she should not be alone. Does she have family? A POA assigned?

Since she hasn't had therapy in a while, you or a family member could call her doctor and request therapy again. Just be aware, that your friend will get worse because of the Dementia and that 24/7 care will be needed eventually. If you and other friend don't feel that you can provide that care, decisions for placing her will need to be made.

So should she be left alone...only you and other friend can determine that. Maybe set up a camera when ur away so you can see what she is doing. Does she pretty much just sit in a chair and watch TV? Can you leave snacks and something to drink near her?

For over a year I had 24/7 for my mother
with caregivers as well as myself. My mother passed away on March 29 so now my dad is alone at 96 years old. About a week after she passed away I ordered cameras and have them set up because he is basically alone. We had more caregivers when my mother was alive and they cooked for both of them of course and made sure he took his medications. Someone needs to be there for him at breakfast lunch and supper and to make sure he gets to bed and takes his medications. We’re down to only two caregivers that come sporadically for an hour or two each day and I am there also when they are not. The cameras have been a godsend. Of course I’m still a nervous wreck because they go off by motion and he doesn’t sit still so God only knows what he did before the cameras were there. Please at least consider cameras not to take away their privacy but for your peace of mind. The camera system I ordered was Blink. We got a five camera system and it ran about $379 and with tax was $402. Well worth it.

Your profile says that your friend has dementia. Her having dementia means that she can't think things through logically. She may not realize her condition. People with dementia have cognitive and physical symptoms. I'd read a lot about what they encounter. Often, it's confusion, loss of initiative, poor balance, weak limbs, lack of coordination, depression, agitation, etc. People who have dementia have brain damage. They often are afraid and confused. My LO would ask me what was real and not real. She needed a lot of assurance that she was okay. People who have dementia are not necessarily lazy. Their brain is not working properly and they may not be able to stay mobile for a lots of reasons, including the brain damage.

Are you the Healthcare POA and Durable POA? If so, I'd request a full assessment to determine the level of care she needs for her mental and physical safety. They need to know the kinds of things she is not doing for herself.

FIRST, as a caregiver for a person in her situation, I'd also get a consult with an attorney to find out what your legal duties and responsibilities are.

Agreed, if sit in chair, food and drink so she can reach it, a bathroom appliance made for women, and a garbage bag, tv, remote and pillow (if she tires of tv and wants to nap) all set.

Do you have any authority to invite anyone into your friend's house without her permission?

By "live in friend and caregiver" - do you mean you hold a paid position whereby you have accepted any sort of formal or professional responsibility for this lady's welfare?

Without one of both of the above, you simply don't have the right to make this decision on your friend's behalf, and "let her be by herself" doesn't come into it. It's just not up to you.

Wow! You are a good friend! She sounds a bit unstable neurologically. Can she be convinced to see a doctor to check out her mental health? I’m not ill, but I’d love to have a caregiver to help me during the day when I am too lazy to do anything.

If she is able, physically and mentally, to get to the bathroom by herself and to get out of the house in case of emergency or fire she can probably be left alone for awhile. It would be too bad if she fell, but it sounds like someone is coming in at some point every day, so she would be discovered in reasonable time.