Honestly, I think the fact that she just held her and said they should head back home is way more powerful to Landlady than immediately saying it back to her. Shows she cares about her and there probably wouldn’t be any “you only said it because I said it/you felt obliged to say it back” line of...
Maybe the author decided to make Yu an Infernal so that he could be the first one cured by Shinra’s return or something else along those lines. Idk, but it kinda feels like he’ll be used to make the readers feel down about seeing another kid getting turned and then some miraculous recovery...