John Calvin Commentary Acts 5:7

"And it was about the space of three hours after, when his wife, not knowing what was done, came in." — Acts 5:7 (ASV)

The punishment with which the Lord punished Sapphira contained nothing new, except that the example was further confirmed by it. And it happened by the sure providence of God that the Church should see separately the obstinate wickedness and treacherous mind of both of them. Since their faults were similar, they could have been exposed together; but it was more fitting and profitable for the Church that they should individually expose their own wickedness.

Sapphira was not prompted by the sight of her husband to deceive (as often happens), so that her fault could be attributed to shame. Rather, acting of her own accord and urged on by no other influence, she appeared to be no better than her husband. Moreover, their wickedness in lying was similar, since she could see from Peter’s questioning that their deceit had been discovered.