My suggestions here are based on experience as an educator; I'm not a teacher of English.
We are trying to help build associations between heard/spoken words and words on a page. This is made more difficult by the irregularity of English, we cannot always predict how to pronounce a word from its spelling. Consider Loughborough: the ough has two different pronunciations in the same word!
Despite being a native English speaker I learned to read many words never having heard them pronounced, and hence as a child would mispronounce them.
In the end all such learning, the building of associations, will come with structured practice. Time and focused effort will be needed.
I would hope somewhere that there are good online courses for this but I'm afraid I don't know of any specific instances. However one idea that occurs to me to help with reading: get audio books and the physical book. Listen to the audio book and read the page at the same time. Then attempt to read the page outloud yourself. I think you will find that this is relatively painless way to practice reading.
Writing I think will be more difficult, I certainly found this when attempting to learn French and Spanish. English has so many words that are pronounced the same but spelled differently (their, there) that even native English speakers struggle.
Again though, using recorded may be helpful. Listen to a short passage. Attempt to write it down. Compare with the text. I often want to prepare a lyric sheet for a song I'm trying to learn. I put on a track, listen to a line or two, then type it, refer back to the track again. Your friend could do this, but for songs that have a reference text online. You may need to be selective about this, literate song-writers who do not use too much slang may be best. (Examples: Al Stewart, Reg Meuross, Paul Simon). Even then, some additional work will be needed to focus on the homonyms; prepare lists of commonly used word variants. (tea, tee; their, there, they're; its, it's) and work to rote learn them.