is she really ugly or is that how she perceived herself?

I think she is plain looking or maybe a bit ugly in the story like compared to her sister of the blond haired girlie

But the author might not want to like draw someone to be ugly and pain someone in real life.

i think she is just average looking but because of being bullied all the time growing up as well as physical and verbal abuse form her and being compared to her sister she feels as though she is ugly and unsightly.