Am I Allowed to drop my brother's wife by car to her parent's home?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

If there is a third person with you, it is lawful that you drop her by car at her parents’ home.  Otherwise it is not allowed because it is unlawful for the Muslim to be in seclusion with an alien woman.

The Prophet (Sallallahu Alaihi wa Sallam) said:No man should ever stay in seclusion with an alien woman and no woman should ever travel unless accompanied by a Mahram (unmarriageable man).[Reported by Imams Al Bukhari and Muslim].

Allah knows best.