*Edit* I just saw that you both are using iphones. Well if you 2 are using the same AppeID then it's clearly the reason. Are the messages blue or green? (blue means iMessage and green SMS). Text from iMessage are automatically replicated to every device whith imessage on. So atm i see 2 solutions: 1. Deactivate iMessage on both or only 1 device (under Settings > Messages -> iMessage) or 2. Create a new AppleID Account for you or your wife.