@Talh
That sounds more like cullinaire is personally upset about it, and is not thinking about the characters and their positions. If Sherry just starts ripping into her senior over that the likelihood she'd potentially damage her relationship with her senior (the one who their master let decide if they got her at all) and her new owner (who is clearly enamored with Roxanne) would increase, potentially landing her back at the slave market. Even if we know the MC wouldn't necessarily do that, it would have to be a concern of Sherry's, because that's fairly sensible.
No doubt she's been truly well mistreated in the past, so if she can't handle a bit of unintentional ribbing (unintentional judging by Roxy's face this time), it wouldn't make any sense at all.
Now, if she took Roxy aside and talked with her about it like say, sisters, I'd say that might even increase their bond and understanding, and make Roxy feel even more inclined towards her. Instead of some guy getting angry that someone pointed out the loli doesn't have tits.