i think its just a beauty standard of the time, paula is described as having large eyes with soft features(which is beautiful, its just the freckles holding her back), her sister just has sharper features, at the end of the day her sister is beautiful so obviously she would be too just in different ways, i say this as a novel reader!
Ppl not only where she grew up called her ugly, others outside did too. So as a character, she's written as ugly even if she didn't look it to us. And like the reply before me said, she'd an unreliable narrator at best, living inside her own mind and exaggerating ppl's reactions to the max. Also, it's worth noting that the author is Korean, so what count as beautiful should be filtered through there eyes as well.

i do have a question for novel readers, is paula actually canonically ugly and the manhwa just made her a lot prettier or was it that the entire time she was pretty and her family/peers were just insulting her to make her feel bad? cause even season 1, she wasn’t ugly. shes a skinny girl with slanted eyes i really did not get it but maybe it’s a manhwa thing