I think there’s a big difference with “practicing” sentences with your wife where neither has a good accent or the best ability to spot mistakes or knowledge of the word the other person doesn’t know (though I have no idea how much or how good the GP’s practice was), and practice with a native speaker (or even better an actual teacher too) who can quickly tell you about mistakes and unknown words to give faster feedback and more deliberate focused practice. I’m not at all surprised that GP’s Spanish is much better than their French.