ABS light

You have big problems. That contamination will ruin every piece of rubber in the system. If you haven't driven it yet, get it all out ASAP and flush the system with fresh brake fluid. If the car has already been driven, then your going to have to replace every single component and hoses in the brake system because they all have rubber inside of them.

That is what my mechanic said. He flushed the system, replaced the master cylinder and drove it around, the ABS light went out. Walmart changed the the oil and topped off fluids. I am fighting with the ins. co to be reimbursed for replacement of MC but they say we waited too long. My daughter didn't notice a prob til 3-4 wks later. when she had to brake hard and ABS did not work. Wondering if she should have noticed a problem right off.

I wouldn't take that answer at all. It doesn't matter how long it took to develop symptoms. They caused the problem and they are responsible. You could see problems developing for a real long time if everything isn't changed at once.