Sure. Soon™.
Why would she react that extremely for something she barely knows about?
The slums shrinking isn't necessarily good or bad without further context. If it's shrinking because people are pushed and thrown out, it's probably bad. If it's shrinking because people get better living standards, that's good.
Is a caterpillar so scary she has to flip her shit and everyone else's? How sheltered is she? And she's even a maid...
Why is it necessary for the manga to spell out which situation it is? It's some version of the former, it's obvious enough, and that's all that matters. Why would the manga have both of them react as if the slums shrinking is a sad and morally terrible thing, if the case is that their living standards are improving? You're just being pointlessly pedantic when it's already self-evident.
As for the maid, I'd say she was more surprised than afraid. You don't see her continue to be freaked out. And even if she is a maid, she clearly comes from a higher social background because she's waiting directly on the Saints. Probably a daughter of skilled tradesmen or merchant family. As a girl, she would still be relatively sheltered, and she would be distinct from servants drawn from worker families and do more menial work like cleaning.
In some societies, the maids who waited directly on the nobles of the house may even be lesser nobility, due to the need for decorum and privacy, and while usually they were called and distinguished as 'handmaidens', sometimes they would wear maid uniforms to indicate their subordination to the working hierarchy within the house, even if they had a higher social status outside the house than say, the head servant. That isn't the case here based on past chapters, but I would highlight how just saying 'she's a maid', doesn't really explain anything.
Is that what the author had in mind exactly? Maybe not, but I have this peeve when people's first reaction is to nitpick something when you can form a perfectly plausible explanation in 5 seconds and put it out of your mind. Like, why didn't the eagles simply carry Frodo to Mt. Doom? Well, why does Tolkien have to spell everything out? Obviously they couldn't...and that's that.