He thought simply giving her freckles made her ugly, and that other people wouldn't like her because of it. If that's how he thinks others are, it must mean that's how he is too, or else he never would have thought that. Remember, the whole reason he fell for her in the first place was because of how beautiful she is. Also, in this chapter, he made a point of acknowledging how beautiful she is, right before she got her allergic reaction. I feel like that was done for a reason. I'm thinking that she'll probably swell and and break out in a rash, and Parker might be end up saying something insensitive or express disgust or something (everyone else probably will too). And with Curtis off sulking because she's trying to reproduce with Parker, that will leave the door open for Winston to come in, who won't be turned off by her appearance (especially with the way she's not turned off to his scars), which will lead to her developing feelings for him.
I think she's having allergic reaction to the wheat
Σ(  ̄□ ̄||)