A good analogy for this would be a fighter pilot on the Western Front in WW 1 in 1916/17. If you survive long enough you develop that inner sense to tell you when somethings wrong and when its right. Yes a whole lot got killed but once you learned the lessons you were the one doing the killing and surviving. This is the ultimate survival of the fittest and Tatiania is one of the fittest right now.If you're frustrated because "the Germans didn't kill all snipers and it's unrealistic," then I hope you don't open a history book or even a Wiki page on snipers.
What do you want the Germans to do, exactly? Snipers are hard to counter even in modern times with all the thermal optics, unmanned drones, and other fancy tech. You can be improbably good and stop 90% of snipers, but the rest like Tatiana get lucky and survive until they aren't lucky and are hit. The Germans are likely doing what they can, which might be a lot but historically was rarely enough.