My friend, whose account is on the lemm.ee instance, is able to post to lemmy.world and lemmy.ml communities as demonstrable here
However, another friend, who is on lemmy.world, said that her posts aren’t showing up on lemmy.world.
https://lemmy.world/c/askmen?dataType=Post&sort=New
https://lemmy.world/c/askouija?dataType=Post&sort=New
https://lemmy.ml/c/askgermany?dataType=Post&sort=New
Her posts haven’t been removed, otherwise they would’ve shown up in the modlogs https://lemmy.world/modlog?page=1&actionType=All&userId=999488
From what I am seeing, your “friend” is not the kind of person you want to be friends with. Maybe it is time to find new friends.