First bring her into your home. In the familiarity of home, normal moral boundaries are reasserted. Let her shave her head, and sit in mourning for a month. By month's end, the moment's passion has faded. But first I'll give myself 24 hours to think it over.
Human beings are capable of all kinds of higher reason.
We can split the atom and land a rocket on Mars, but sanity and civilization are a delicate edifice of reason over a maelstrom of envy, insecurity, and terror. One night, a guy is driving alone far out in the country. The bolts holding the wheels of his car become loose, and eventually one wheel comes off. The car careens into a ditch. With no phone or dwelling in sight, the driver is at a loss.