what does 'She will make me a good wife' mean?

You are right. It depends on the context. Situation #1 : A man sees a woman, and keeps watching her movements and behavior. It is possible that he finds her good "wife" material. Then this statement can be used to express his feelings, at that moment, and the meaning is clear. Situation #2: A woman who is hoping to marry a man but is afraid whether she will really fit in his family. Then she finds say the mother-in-law/or sister-in-law quite friendly and iclusive. Then even though she nurtures doubts as to whether she fits in she could conclude about one of the womaen this way with emphasis as shown. [B]She[/B]{MIL/SIL, say} will make [B]me[/B] a good wife. But the second meaning in my opinion is most contrived and mathematical rather than being linguistically right. This is an example of beinggrammatically right and usage-wise not appropriate.