It's not THAT simple, Todorova was never considered a good skier IIRC. She shot 10/10 in Nove Mesto sprint last season and finished 1:45 Min behind Herrmann who also shot 10/10. Eckhoff shot 8/10 and was still 34 secs. quicker than Todorova. Hell, Regina Oja and Merkushyna has faster skiing time back then, hardly world beaters in terms of speed.
Today she finished roughly 45 secs ahead of Herrmann who shot 8/10 so probably would have finished fairly equal to each other if Herrmann shot clear.
So in a matter of 12 months Todorova has gained well over 1:30 minutes to Herrmann' skiing time which is quite impressive.