I did a little reading up on this. I'm assuming by the 412, Mass, that you live there.
In Massachusetts even used cars sold by a private person are covered under a lemon law. If the car fails to pass inspection within 7 days of purchase and fixing it is greater than 10% of the purchase cost, the buyer can void the sale. The Lemon Law also covers this in a different way. If within 30 days of purchase, she can prove that you sold her a car, that had a defect but failed to disclose it, you would have to refund her her money, less a slight mileage charge.
Since it was longer than 7 days before she did the inspection, she can't do the first, and since you say you didn't know about the problem with the control arms, and obviously she can't prove that you did, she is shit out of luck.
All this said, I'm not a lawyer and don't claim to be, and my advice is given as is. Just do a quick search on Google for this and you'll see what I'm talking about.