Last living parent died while I was living with and caring for her. What rights and limitations does sibling with POA have?

POA expires at death and is now meaningless, is your sister also the executor/administrator of the Will? If so sis has a duty to follow your mom's wishes as written, if there is no Will then your state will have a formula to determine how any assets are distributed (generally if there are no other close relatives then after expenses and debts are paid you would share equally).

Shadowwatch, my heartfelt sympathy to you and your family.

Your sister is no longer Power of Attorney for your Mom. Once Mom passed, the POA passed, too. Now it is up to the Executor of the Will to do their job regarding the estate.

If you live in the States, you might want to check to see if your Mom's Will needs to go into County/City Probate Court, thus nothing can be done until the Probate Judge signs off on the case as closed. If there is no Will, then the Probate Judge will decide who gets what according to State laws.

So hold off on the estate sale and the selling of the house until the Executor has time to figure everything out and to see if the Will, or no Will, goes into Probate.

Regarding your rights as your Mom's caregiver, unless your Mom had put something in writing and it was attached to her Will, sorry there isn't much you can do now. If the Will goes into Probate, you might be able to plead your case to the Probate Judge.

POA died too. I am sorry for your loss. Who is named as executor in her will? Be patient settling an estate takes time. Try to work with sis. Do you have someplace to go? Do you have a copy of the will?

All of the above is true HOWEVER if your caring for your mom kept mom from having to go to a NH in some states you would now have a life estate in her home. Of course you would have to do all the upkeep etc of the home, pay the taxes and insurance.
See a certified elder attorney for advice on your states rules and what rights if any that you have.
I’m very sorry for the loss of your mom. I hope you and sister can work things out.

I'm so sorry for your loss shadowwatch.