I'm definitely not happy, especially the way her insurance handled this, lying to me it's 70/30 and that it's final and then changing it to 50/50. When the accident initially happened, I felt bad for the woman, because I was pretty sure it was her fault and that if she was a little bit more alert it would not have happened. I still don't have any beef against her, but I do against her insurance now.
If it was truly "final" you would not have any basis to contest it.
You contested their decision - which opened it up to change either way.
Unfortunately for you, you revealed a truth that was not in your favor: you had a stop sign and she did not. Because it is unlikely that she was flooring it like a bat out of he77, they concluded that you failed to yield.
You should take particular note of what Highwayman and CdwJawa stated.
You should also notice that the more you tried to justify yourself here, the more fault was ascribed to you, just as happened with the insurance.
I strongly suggest that if you choose to sue the other party, that you hire a lawyer. However, because the damage to your car was minor, it might be cheaper to just accept whatever you can get from the insurance.