。
She rolled the dice on it, knowing full well she might lose a fortune.
Literal
She [topic-は] large-amount [genitive-の] money [object-を] lose might [quotative-と] aware [on-top-of-の上で] all-or-nothing tried.
Two notable idioms. 承知の上で ('with full understanding / fully aware that / knowingly') is a set phrase — [clause]+(という)+承知の上で marks acceptance of a known risk. 一か八か ('all or nothing / sink or swim') is a colorful gambling-metaphor idiom: literally 'one or eight,' from a dice game where 一 ('one') and 八 ('eight') were potential outcomes — 'do or die.' やってみる is the te-form of やる ('do') + みる ('try'), the standard 'try doing X' pattern.