How close are you to this relative? If it was one of my relatives I would offer as much time as my work schedule allowed. Get them as much as I could and ask to keep one for a family heirloom. Then again are we talking a safe full of single shot shotguns and JC Higgins 22's or is it Colt's, Winchesters and war trophies? But regardless it's family and you should help family out. Put the she on the other foot...
Now to answer your question, an estate auction at her house will yield the most bang for her buck if these are high dollar items. If just run of the mill stuff then take them to a few gun shops and see what she can get.