I've read about this in the past. The problem seems to arise when using cross platform products. You receive SMS on the Android phone, but are now receiving iMessage on the iPad. Once an iMessage has been sent/received with the iPad, it seems it will associate the phone number and email both with iMessage, therefore creating an issue with your wife sending you a text. To be honest, I've not seen a resolution posted about that. I recommended to one person to try deregistering their phone number with iMessage, but I've not received a response if it works. Unfortunately, if you disable iMessage on the iPad, you will not be able to text your wife, since you cannot use the Android phone to forward to the iPad, like you can with an iPhone.
You may have to run this by Apple Engineers to see if there is a resolution. I see this being something difficult to resolve.