If you are going to use the parable of the wheat and the weeds, it may be best to know the Watchtower "explanation" for this parable.
Commenting on Matt 13:24-43, this is what they write in their Trinity brochure page 9: "Jesus himself explained what was behind this falling away from true worship. He said that he had sowed good seeds but that the enemy Satan would oversow the field with weeds. Thus a deviation from true Christianity was to be expected until the harvest"
All this is under the subheading "Apostasy Foretold", and as one can see, the "exposition" provided is to satisfy the Watchtower abhorrence of what they call "apostates". That's us, by the way. The Watchtower is telling us here that Jesus foretold a time when many who once bowed down before the Governing Body of the Watchtower would fall away. Hmmm...The question is: Is that what the parable is about?
You are going to have a tough time convincing your wife otherwise, if as you say she is in deep in the organization, since what the Watchtower says is regarded as gospel truth. But you may consider:
1 The word apostasy is not even mentioned in the parable, neither is its concept.
2 In order for those who symbolize the weeds, to be "apostates" it must first be shown that they were wheat originally, and then became weeds. This is absurd, as the parable shows. The wheat are always wheat, and the weeds are always weeds. It is obvious that what Jesus is referring to are not apostates, but counterfeit Christians. They will always look like wheat, and act like wheat and talk like wheat, but they are still weeds.
3 Thus ever since the birth of Christianity there will be counterfeits proposing all sorts of ideas, and naming all sorts of names, but that of Christ, these will be identified in the end.
4 The Watchtower teaches that by the 2nd century AD, a major apostasy broke out in Christianity, and the first evidence of this was the removal of the name "Jehovah" from the NT manuscripts, and the corresponding emphasis given, unjustifiably, mind you, to the name of Jesus. This apostasy would last 18 centuries, during which time True Christianity would disappear, except for scattered groups of unnamed true worshipers. This situation would last till 1879, when CT Russell would start the Watchtower system of belief.
5 If this is what the parable of the wheat and the weeds symbolizes, then: the wheat would have to completely disappear to be overrun by the weeds. This is simply not so. The wheat stands tall and unconquered, it is never overrun by the weeds. In fact the weeds are kept isolated, so that they may be burnt in the Day of the Harvest. This parallels Jesus promise to His church that it would never yield to any outside force. Despite its imperfections, despite its inner quarrels, despite it all, it will always exist as a free institute under Christ.
6 It must be noted that True Christians have no part in the harvest work. That belongs to Christ alone. It is not our place to persecute or in any way physically abuse these counterfeits. They must have their day.[Matt 13:42]
Hope this helps.
Cheers.