Nah, Auntie is just testing her resolve.
Thing is, I'm getting the sense that Auntie here is the current matriarch of the family.
This is actually Pretty Goddamn Serious(tm) in Japan's hierarchal structure. Papa might bring home the bacon, but within the confines of the home? Mama rules with an iron fist.
And when you're the Mama that rules over all the rest of the Mamas in the family? Then each and every one of those family units is under your purview.
Now. She may not actually wish to cause any strife. But in order to ensure happiness within her family? She will not abide a weak-willed woman to marry in. Steadfast devotion is what she wants in the wives in her family. A strong will that will carry them through when times are tough. Mentioning the idea of setting Yuu up with her own son is a quick and easy way to test Yuu's resolve.
And it looks like Yuu-chan is meeting up with expectations splendidly.