For what it's worth, I used to teach English internationally. The students who were the best at English had found something they were passionate about and practiced a tonne. For example, some students liked to play games online where it was required you spoke to people, some loved English music, some loved documentaries or certain film genres. If there is something your partner is passionate about, maybe they could sign up to a local club and practice there! I think the key is that it shouldn't be 'work', just something positive to focus on in English.
I do understand that finessing grammar is slightly different, but these kinds of activities do help a lot, especially if you're able to speak to native level speakers (which I imagine will be very easy to do now!) Just my two cents anyway