Can I find out for free power of attorney on my sister?

Need more details: what's going on with your sister? What state do you live in?
When you say "find out for free" do you mean get the forms and how to go about getting PoA? Try contacting your local area's Council on Aging as they have many resources.

You could probably download some very basic forms online for free but they may not be written for your state's laws and rules. For a minimum cost you can go to Legalzoom.com or Rocketlawyer.com and get the forms specific for your state and also some basic guidance and info. That's what I did. Good luck!

I agree, call Office of Aging. There is legal aid that can help u with this.

Be aware that you can't get POA if Mom is incompetent to assign you. I would not download forms. Have a lawyer or Paralegal help you.

Go to your public library and check out the latest copy of the Willmaker software. Then it'll walk you through the process of making a POA or a will or a trust. If you've ever used turbotax to do your taxes, the process will be very familiar.