Sister controlling and intervening when it comes to my mother. Mother lives alone and is not incapacitated. Sister has issues with me. Advice?

If your Mom is competent unless the DPOA is immediate, your sister has no control over Mom. POA usually don't come into effect until the person is declared incompetent to handle there own affairs.

Is your mother in her right mind and she is complaining to you that your sister is not allowing her to live her own life? If she has all her mental faculties then the sister has no legal authority to "control" her. But if she has cognitive issues such that she cannot make decisions in her own best interests, then maybe what others interpret as "controlling" is actually the sister carrying out her directive as PoA. Can you provide more information to the forum so you can get the best advice?

If your mother is not incapacitated then if she wanted to I’m pretty certain she can remove your sister as her DPOA.
If your mother is not happy with her POA choice then she can do something about it.
However, I’m wondering is it you that’s not happy with sister being DPOA or your mother?