Aye, it's abuse. Abuse of the system. Abuse of the mentality of your brother. It'd be in your brother's best interest to leave this woman. She sounds like the lying deceitful type that can be no good to anyone.
If she's quick to lie about something as silly as using one's car, then I can't see it being far from lying to get the upper hand in a domestic violence, false rape, child abuse, etc.
Women like this give good women a bad rap. I despise them.