The answer is: She demanded Hagar and Ishmael be sent away

Genesis 21:10 - Sarah saw Ishmael mocking Isaac and demanded that Abraham send Hagar and Ishmael away, which Abraham did reluctantly after God told him to listen to her.

In Genesis, the story of Sarah, Hagar, Ishmael, and Isaac weaves a deeply intricate tapestry of family dynamics, all set against a backdrop of divine promise. When Sarah witnessed Ishmael mocking her son Isaac, her reaction illustrates a mother's fierce protection for her child. It’s quite a dramatic moment—after decades of waiting for her son, it’s no surprise that Sarah’s patience frays upon seeing Ishmael’s derision.

It's intriguing to note that this moment intersects with larger themes within the Abrahamic tradition of sibling rivalry and competition for inheritance, which can be seen in other stories, like the feud between Jacob and Esau. Notably, Hagar's name means "stranger" in Hebrew, highlighting her outsider status—making Sarah's actions somewhat more significant. In the ancient cultures surrounding the text, honor and lineage were paramount, so Sarah’s demand wasn't just about personal emotions; it was a move to secure Isaac's rightful place.

Interestingly, God reassures Abraham, telling him to heed Sarah’s request, which underscores the respect for her authority in that patriarchal context. This reflects a fascinating biblical principal showing the importance of female voices—even in society's silenced narratives. In later scripture, despite Ishmael's banishment, divine promises regarding him were also fulfilled; he becomes "a great nation" (Genesis 21:18), showcasing an overarching plan that embraces both sons—Isaac, the child of promise, and Ishmael, who symbolizes God's wider care for humanity, even outside the conventional line of blessing. Moreover, as we see these narratives play out, they echo in many ways relational struggles found in our own lives across faith communities.