I recommend downloading Discord to join an English Language Learning server.

The voice chat rooms allow you to speak with real people to improve your listening comprehension. The text chat rooms will improve your reading and writing.

There are many native speakers there that enjoy helping, myself included. It’s not “gamelike”, but nothing is better than talking to real people - I’m sure you’ll find value in it.

Well now I'm intrigued by what your native language could be.

Maybe look for peer to peer type setups. Iirc Babel has one. Basically you’re just chatting with someone else. Iirc they also have a live class thing, which might be good too.

Personally I’m using Duolingo for Spanish, along with watching movies/shows in Spanish (still at kid level so cartoons mostly) and a site (who’s name is escaping me right now) that has a ton of videos that range from very simple to much more complex.

Play video games in English. Watch English-speaking YouTubers. Interact with people online using English. As long as she enjoys the content, proficiency in the language will follow.

pirate movies and watch them. This is the fastest way to learn a language.

Can I ask what your native language is?

I've found that ChatGPT4 is an excellent tutor and can create a good learning plan based on your specific level, almost any subject (including English).

Often you can explain stuff in your native language to it, if you don't know the English word for it. 🙂

Anki is a flashcard app that can help with memorizing vocabulary.
Watch media in English with your local language as subtitles. Or the opposite.

honestly, any app that is in english and keeps her engaged. There are penpal apps, where you write people letters. or maybe something like microblogging or lemmy.

if you can pay the Rosetta Stone is the best. None of these free apps come close to it in my opinion.

Find some teachers of the language on YouTube. Watch short videos daily. Since they are teaching the language it will be basic and you can use subtitles and speed to make it easier and hear and read at the same time.

Do this for a while until it is too easy then move on to world news in the target language again on YouTube and or on a site in English. As it is world news the events should be familiar.

Then move on to movies with subtitles .

The most important thing is daily contact with the language. Listening is the most important part as you need to understand first before you can begin to respond. It helps you structure the language and learn how to construct it.

Has your SO tried books? Ebooks or audiobooks could be helpful. They could try reading a book they are already familiar with in english, that way they wouldn't have to put too much effort into getting acquainted with characters and plots, and focus into pronounciation, grammar and slang.

Ginger Writer can analyze and improve written text in English.

Talking about apps I would recommend MosaLingua (digiSchool), it helps me for English and Spanish.

It's mainly design to learn vocabulary (spaced repetition), the app is free, only class/courses may required a subscription.

Answering your initial question you can select the "native" language you want, but I'm afraid you won't find your mother tongue.

The best way to improve her English is for her to read tons of English literature.

Get her a Kindle Paperwhite (about $120) and encourage her to read fiction. It has to be enjoyable.

With the Kindle, she can look up the dictionary definition and pronunciation of any word she encounters and does not know.

Busuu is neat. It has a feature to submit answers to the community so native speakers can correct speaking/writing and give tips.