Apologies it was left out, that's edited now.
We've accepted it as an approximate answer but the completely correct answer is the one above using 'she has'
'She wrote to him' would be better translated as
either 'Ysgrifennodd hi ato fe' (South Wales)
'Mi wnaeth hi ysgrifennu ato fo' (North Wales)
So why have you added it as an acceptable translation? It will teach us learners that we can use the perfect tense formed using wedi in the wrong situations.