FM, If I had to make this decision I would think long and hard about what it would be like for not only me but more importantly my kids to be stuck with this raving lunatic on a long car ride.
To me, it would be worth any amount of $$$ to send her crazy self-absorbed @$$ packing on an airplane so I could have a peaceful drive home and quality time with my children.
But, you know your finances better than I do.
Remember, the non-monetary price of her presence might be higher than the cost of the ticket, to all of you.