Because if she didn't tell him, and he found out on his own, it would have been BAD.
I'm sure she left out the part about them trying and failing to fuck lmao.
She's putting herself into a self contradicting feedback loop, you can't force yourself to have a relaxing day off as research for work, because that research counts as working!
I've read this chapter several times over the years but there's one scene that's always confused me. When Anzu comes by the game shop to play with Yugi, did she actually come up to his room and help him with the puzzle for a while? Or did she get weirded out by grandpa and leave right away? It...