。
She says it's my fault our marriage isn't working out.
Literal
She [topic-は] married-life [subject-が] doesn't-go-well [nominalized-のを] me [possessive-の] fault is [quotative-と] says.
A two-step embedding: the inner clause 結婚生活がうまくいかない ('the marriage isn't going well') is nominalized with の and marked as the object of the outer verb 言う ('says'). Inside the quoted content, ~のせいだ ('it's because of / it's the fault of') assigns blame for a negative outcome — paired with ~おかげで for the positive counterpart. うまくいく ('go well, work out') and its negation うまくいかない are the standard collocation for projects, plans, and relationships succeeding or struggling. The dictionary-form 言う in narration suggests habitual or characterizing speech — 'this is what she keeps saying.'