Unfortunately not having a blessing will be a giant burden and a stigma on Lucina's shoulders for the rest of her life. Shizuru might be able to make her forget it for a while, but sooner or later she would get depressed by it again. Aside from Shizuru actually making her manifest a blessing that just wasn't discovered earlier, the only thing that would make her feel better somewhat more permanently would be if her own future children all turn out to have a blessing normally. If they were to be born without a blessing, it could be the final nail in her coffin.