。
She was passionate about music.
Literal
She [topic-は] music [object-を] passionately was-loving.
熱烈に ('passionately, ardently'), built from 熱 ('heat') + 烈 ('violent, intense'), brings literary intensity to whatever it modifies — 熱烈に支持する ('support fervently'), 熱烈に歓迎する ('welcome warmly'). 愛好する ('to love, to be devoted to') is the formal Sino-Japanese verb for 'be a lover of [X]'; it's the language of liner notes and obituaries rather than casual conversation. The ~ていた past habitual frame paints this as a sustained, lifelong passion.