Any POA should be filed in the Real Property (Formerly Deed Records, now Official Public Records) in whatever County your Aunt owns surface, mineral, or royalty rights in. It can be an original POA or a Certified Copy from a County that it has been previously filed of record in.
Once it is recorded, whichever you sent them will be returned to you.
Having said that, you should contact the Attorney that put together your Aunt's Trust Agreement as to whether a simple POA will allow your Aunt's Daughter to sign anything on behalf of the Trust. She may need to be appointed Substitute Trustee or anything she signs may be invalid.
Hope this helps -
Charles Emery Tooke III
Certified Professional Landman
Fort Worth, Texas