What's your least favorite smell? Garbage? Farts? Axe body spray? For Anna Frith, the answer to this question is "none of the above." Her least favorite smell is rotting apples.
We know this because she says so, like, a billion times. We watch her get overwhelmed by the stench as she walks through the apple orchard, noting that "there are so few people to do the picking" these days (1.1.2). Anna once loved this smell, as it was always associated with the fall season, but now she just thinks about the plague whenever it hits her nostrils.
For Anna, then, the "sickly sweet smell" (2.2.67) of rotting apples becomes a symbol of the decay caused by the plague. It becomes a reminder of how things that once brought comfort can now bring pain. Eesh. We don't know about y'all, but we're not going to be in the mood for a fresh Fuji or McIntosh anytime soon.