...the thief just always has the worst things to say, doesn't she?
I could be generous and say she wanted to make Shin feel useful... but I would expect, after they talked through things last chapter, she would understand that is not the actual way to get him willingly travelling with them again
Just say that even when he didn't seem as useful, you enjoyed adventuring with him, and the only real reason you decided to kick him out was worrying he might have gotten hurt. That was working well last time, and isn't even a lie!
This feels like the author either writing her inconsistently, or actively trying to undermine her so he can continue with the scenario being "forced boob rape".