musashi won't try to humanize shuten to her since that's not really her place, but she can at least soothe shinobu's ego a little by assuring her that musashi only *barely* beat shuten in their duel. hell, idk if you've read the shimosa arc of fgo, but musashi barely survives *all* of those fights.

but also she can call shinobu pretty and flirt with her, that's ego medicine too