[Child of the 7th Age]

Her thesis is that in the Old Testament/Hebrew Bible, the satan was merely an adversary of humans, doing God's will to challenge or test us

I concur. As someone who has more familiarity with the older Hebrew texts than the Christian Bible, I can tell you that this is how Satan is still presented within the Jewish tradition. In the rabbinic tradition, there is far less emphasis on Satan as an external force and more emphasis on the struggle within the human soul between the yetzer hara, the so-called "evil inclination," and yetzer hatov, the "good inclination."

But neither of these entities in the soul are totally evil or good.... That would take a lengthy explanation which would not be directly relevent to this thread.