All of the above is very sound advice. I would take the time now to look at the major gun auction houses and see what similar guns have been listed for and what they actually brought at auction. Typically the auction house charges between 10 and 17 & 1/2% to the seller based on the hammer price. Most of the major auction houses have their past sales & prices realised on-line. By posting them now yourself on Dave's site (selling cost only $10.00 per gun), Guns International or Guns America & selling them yourself you will probably realise more money but it will, of course, take longer. Depending on what you have will largely determine how marketable your collection is. To leave this up to someone, like your girlfriend, who is unknowledgeable about guns is only asking to get ripped off, in my opinion.
Just My Thoughts, George