Excursions that require waivers with child who is not yours

[gluecksbaer]

Has anyone taken a child for whom they were not the legal guardian on an excursion that required a waiver?

I'm considering sending my daughter with her aunt on a zipline excursion in Rotaan, most likely through Royal Caribbean.  But I'm wondering if there will be issues with my sister signing the waiver since she isn't the legal guardian.  

I know this is going to be provider specific, but just wondering generally if people seem to care or if they just want a signed document to point to later.

[topspot]

We have taken a friend of DD on a cruise, and have had to sign waiver for  cruise line excursion.  We were not questioned that she wasn't our child, but we did have a notarized letter from her parents allowing us to take her on the cruise.  

[gluecksbaer]

Thanks!