What are the procedures for getting a power of attorney for my sister in state of Oregon

Hello.
Your sister must voluntarily GIVE you a power of attorney, and she must have the capacity to sign the document. If you are asking for the ability to assist her because she is incapable of making her own financial decision, and she does not sign a power of attorney for you to do so, then what you are talking about is called a "conservatorship." An estate planning attorney in your area can assist you with either avenue.
Good Luck.