真的希望你幸福 , 真希望妳幸福兩句都可以 , 但是語氣不一樣.
Both ok but meanings are a little bit different.
真的希望你能幸福 , 真的希望你可以幸福 - 有"的" , 表示真心祝福.
Having 的 means a real wish and really hope something. Sometimes slightly be used in the situation "she isn't happy at the moment" but it depends on intonation .
真希望妳能幸福 , 真希望妳可以幸福 - 少了"的" , 有時候有同情的味道 ,表示現在他並不一定幸福.
Lacking 的 sometimes be used in situation which is "she isn't happy at the moment" . It indicates that she/he isn't happy at this moment so you really hope she/he can be happy.