I believe you are conflating two things, the one has no direct relation to the other, they simply happened at the same time, probably to add a certain urgency to the plot and leave Nick floundering without anyone to really explain how the Grimm world works. The Grimm powers are clearly genetic in some fashion, the expression of the powers however are unpredictable in terms of when they become obviously apparent. It is clear Nick is starting to see unusual things at the start of the episode and Marie when she turns up is saddened to learn that Nick has the Grimm power but at no time does Marie say that (as far as I can remember) because she is dying Nick is getting her powers.
Doctor: You betrayed me … betrayed my trust. You betrayed our friendship, you betrayed everything that I’ve ever stood for. You let me down!
Clara: Then why are you helping me?
Doctor: Why? Do you think I care for you so little that betraying me would make a difference?
Clara: Then why are you helping me?
Doctor: Why? Do you think I care for you so little that betraying me would make a difference?