She is overflowing with adventurous spirit.

Literal

She [topic-は] adventurous-spirit [with-に] fully overflowing.

満ち溢れる is a compound verb — 満ちる (fill) + 溢れる (overflow). 冒険心 uses the suffix 心 (しん, 'spirit/heart') attached to 冒険 ('adventure'), a productive pattern for abstract qualities.