Not sure what to do.

Welcome, I agree with Susan this is a lot for a young person to take on. I don’t know how you will be able to work and care for her. You are a good person for stepping up like this. I’m retired and my mom is in assisted living and I am still overwhelmed with all that needs to be done. I’m also working on cleaning out her house. I would contact your local commission on aging. At some point someone is going to need a DPOA. If you don’t have it yet now is the time. If you wait too long she may not be willing or able to sign. You will need this to manage her finances and if it comes to it, you may need it to get her into assisted living or a nursing home. She probably will not want to go (most people don’t).
My mom also feels I am treating her unfairly and is not happy with me. She feels I am overstepping and she doesn’t belong in assisted living. People with dementia often have anosognosia. This is an inability to recognize their symptoms and limitations. It makes things crazy difficult. If you go to groups on this website then to new caregivers, you will find a lot of great information. I recommend the staging tool, and understanding the dementia experience. These will help you better understand what you are in for. I tend to be a planner, so I would suggest looking in to a plan B if things become too overwhelming. You can still be a good caregiver by making sure she is in a good place, visiting her regularly while she getting the care she needs in a facility. Just my opinion. This is a great place to share, vent and ask questions of people that really understand.

I would not suggest a DPOA to her with the reasoning that she has dementia and needs it. I would suggest your mom say that she is going to have one done up just to be prepared because you never know and then very casually suggest she might want to do the same. It might also help to point out that a DPOA will not take any of her rights regarding her money away. I was originally very surprised to learn that even now mom can go to the bank and take money out or move it around as she wishes. The DPOA only gives another person access and a right to act but does not take the person with dementias rights away. We just don’t bring her to the bank or give her any credit cards, so it’s us not the DPOA that limits her access.

One thing I like to point out about POA in general is that it's not about disability. It's about having someone else deal with the petty details of life. Rich people use POA all the time—they don't go signing paperwork to buy a car, they have someone do it for them. They don't go to the bank, they have someone do it for them. Creating or using a POA shouldn't be embarrassing for anyone—it's a convenience. The fact that the POA is "durable" doesn't change that.

That said, do not create a "springing" POA if you can help it. In that case a person has to be certified, typically by two physicians, as not competent. This can be a difficult hurdle, depending on the personality and beliefs of your LO's docs, and it really does communicate embarrassing information with every use.

As far as her shutting you down in the dr office,you can make an appointment to meet with him on your own. Explain to him him what really is happening so the next visit he knows. As for the online stuff block things , put supervision control on it. Worth a try.