If a person has created two POA's which one will they go by, in the event that the person can't make their own decisions?

My aunt had gotten some medical poa forms from the dr.office and had me take her down today to have them notarized. She made my husband and I her medical p.o.a, on the way home she said her former sister in law had gave her those kind of papers a few years ago and she couldnt remember if she had them done or not. So my question is, if they in fact had those made up back then which ones would the doctors go by?