、。
Mitsuna is a neat freak, so she often cleans of her own accord.
Literal
Mitsuna [topic-は] cleanliness-loving [because-だから], often oneself [advancing-進んで] cleaning [obj-を] is-doing.
綺麗好き 'cleanliness-loving' is built on the productive suffix ~好き ('liker of X'), which attaches to nouns to characterize someone's habitual preference (例: 勉強好き a study-lover, 寂しがり屋 a loneliness-prone one). 自ら進んで is a set adverbial: 自ら 'on one's own' + the conjunctive 進んで from 進む 'advance,' literally 'advancing on one's own' = 'voluntarily / proactively.' ~ている on the habitual する frames this as ongoing characteristic behavior, not a single instance.