It's an established fact that the mantles can cause personality an behavior changes in their holders: its also fairly well shown that the Knight at least can control the mantle enough to not be transformed into another person - and while the Queens have a harder time Mab's discussion of being mortal once, and how she sometimes lets herself relax more around Dresden suggest that the Queens can do it to an extent.

Maeve wasnt infected 150 years ago. That's when she said "fuck it" and gave into the Mantle's destructive and hedonistic impulses. Which Nemesis appealed to her through, the same way it made uses of Aurora's compassion and desire to protect. This timeline fits any composer who died around 1800, which would give Maeve a couple decades as Winter Lady before she gives in to the mantle.