On the subject of last week's like "You have taken me to London! Don't you know the air here is poison?" This refers to one of my fave debunked old-timey scientific theories, miasma. Miasma is what happened when people figured out that if people went into gross, dirty, smelly places, they tended to get sick, but were nowhere near figuring out microbiology. The idea of tiny tiny tiny organisms living secretly on and inside your body is pretty weird when you don't have powerful microscopes, so back in the day, people figured that it was the smelliness itself that caused illness. Miasma means "bad air", and anyone could see that London had pretty weird looking air back then.
The London fog, to be fair, was full of nasty stuff, but it was thought that the weird-smelling air itself was the bad thing. (You hear this referenced in Sweeney Todd: "Somebody, somebody, look up there!/Didn't I tell you? Smell that air!") The theory was on its way out by the end of the 19th century, but I have a feeling that Frankenstein still believes in it, at least in a superstitious kind of way. Even if she didn't believe it, though, she'd find some other reason to hate London. (Her reasons for this are a bit weird, but it's partly because she's just really not a city person.)