。
She'll make a good wife.
Literal
[topic-は] good wife [into-に] will-become probably.
~になる ('become') is one of the workhorse verbs in Japanese — paired with the conjectural ~だろう ('probably, surely') for predictions about future or likely states. The phrase よい妻になる carries echoes of an older cultural framing where a woman's value was measured by her potential as a wife (良妻賢母 'good wife, wise mother' was a guiding ideal of Meiji-era and prewar womanhood). In contemporary Japan this attitude has shifted considerably, but the phrase still carries faint cultural weight.