A low of -18 C isn't uncommon, but a daily mean of -18 C across a whole month (day and night) is pretty cold! It's colder than any major North American city except Fairbanks, at least. The other cities I think of as being cold all have significantly higher daily means in their coldest month: -11 C in Anchorage, -10 C in Minneapolis, Montreal, and Ottawa, and -4 C in Chicago.
Sure, it gets cold in the winter there, but, say, -20C is not too cold to get out of the house to get some firewood nearby.
I walked at -20C to school as a kid, and it was ok. I wouldn't go out when it was -30C, but considering the mean of -18C, -30C would be rare, and almost never in the middle of the day.
Bottom line: people have lived just fine for thousands of years in much harsher climates, for example, a thousand miles north from where she lives.
-18 C night and day is not that cold. It does not stop any daily activities - like kids playing outside. Going near -30 C and below - with regular "urban" winter clothing - that starts to modify ones routines. Don't look at the statistics, observe the real effects.
It depends on a few other factors, among which are wind and humidity. -18 C in Munich is lovely for a stroll. 8 C on the west coast of Ireland is omfg.
