Actually, the easiest way to explain it is to have your wife read Daniel chapter 4 without the Organizations "bible study aids". The whole thing about the "7 Times" has absolutely NOTHING to do with 2,520 years (using their 'day for a year' interpretation). It's simply referring to the 7 years that Nebuchadnezzar would live like an animal. In fact it tells us this right there in Daniel chapter 4:
"The tree you saw, which grew large and strong, with its top touching the sky, visible to the whole earth, 21 with beautiful leaves and abundant fruit, providing food for all, giving shelter to the beasts of the field, and having nesting places in its branches for the birds of the air- 22 you, O king, are that tree! You have become great and strong; your greatness has grown until it reaches the sky, and your dominion extends to distant parts of the earth.
23 "You, O king, saw a messenger, a holy one, coming down from heaven and saying, 'Cut down the tree and destroy it, but leave the stump, bound with iron and bronze, in the grass of the field, while its roots remain in the ground. Let him be drenched with the dew of heaven; let him live like the wild animals, until seven times pass by for him.'....... Seven times will pass by for you until you acknowledge that the Most High is sovereign over the kingdoms of men and gives them to anyone he wishes. 26 The command to leave the stump of the tree with its roots means that your kingdom will be restored to you when you acknowledge that Heaven rules. 27
33 Immediately what had been said about Nebuchadnezzar was fulfilled. He was driven away from people and ate grass like cattle. His body was drenched with the dew of heaven until his hair grew like the feathers of an eagle and his nails like the claws of a bird.
34 And at the end of the days M[the end of the 'seven times] I, Neb·u·chad·nez´zar, lifted up to the heavens my eyes, and my own understanding began to return to me; and I blessed the Most High himself, and the One living to time indefinite I praised and glorified, because his rulership is a rulership to time indefinite and his kingdom is for generation after generation. . ."
This scripture---absolutely essential in the JW theology about the tree representing God's Kingdom and that that 2,520 years would pass until Jesus started ruling "invisibly" in 1914 is plain nonsense. There is absolutely NOTHING in the book of Daniel to indicate it's referring to anyone else besides Nebuchadnezzar......there's nothing to insinuate that the 7 times means anything other than the 7 literal years that Nebuchadnezzar was bonkers eating or smoking grass and living like an animal. In fact, for anyone who has the WT CD ROM, if you look at verse 34, after the word "days", there's an "M". If you put your cursor over it, it references Daniel 4:16 which says:
"..... Let its heart be changed from that of mankind, and let the heart of a beast be given to it, and let seven times pass over it...."
So, even by the Society's own hand, the "seven times" was completed not in 1914, but rather at the end of 7 years when Nebuchadnezzar had his understanding restored to him.