。
It was unavoidable that her attitude was a bit ambiguous.
Literal
She [topic-は] a-little ambiguous attitude was [nominalizer-の] [topic-は] was-unavoidable.
やむをえない (やむを得ない, 'unavoidable, can't be helped') is a set expression where やむ ('to cease') + を得ない ('cannot obtain') = 'cannot be stopped.' The の nominalizes the preceding clause ('the fact that her attitude was vague'), and は marks it as the topic of the judgment. あいまい (曖昧, 'ambiguous, vague') is a na-adjective.