。
She thought she was pretty attractive.
Literal
She [topic-は] herself [subject-が] [pretty-けっこう] attractive [is-だ] [quotative-と] thought.
けっこう is one of those wonderfully slippery Japanese adverbs — written 結構, it can mean 'quite, fairly, pretty' (positive intensifier) or, depending on context, 'no thanks, I'm fine' (polite refusal). Here the 'pretty/quite' reading is locked in by the adjective 魅力的だ ('attractive') that follows. 魅力的 ('attractive, charming, captivating') is built on 魅力 ('charm') with the adjectival suffix ~的 — productive across countless concept words (具体的 'concrete,' 効果的 'effective,' 一般的 'general'). The と思った frames the assessment as her own subjective judgment.