That 1972 dictionary is a classic move! You need the official Scrabble dictionary, the one updated with all the new words. Arguing won't work, just get the current book and make it the house rule. Once she sees the official source, her challenges have to stop. It saves so much time and ends the debate for good.
Remember my buddy tried that with his mom. She just said her 1972 book was the "real" dictionary and refused to look at the new one. Some battles you just can't win with logic.