If she was not injured, let her insurance company handle any claim from the other driver. If she was, she should get medical attention as appropriate and call a personal injury lawyer in her locality. Watch out for legal time limits.

The thing here is what you wrote: "making a left turn on a yellow light." Are you SURE about the color of the light? Because if it was yellow, then your mother was primarily at fault. This is the #1 most common mistake people make on the roads. They get caught in an intersection and they think they have to clear it before the light turns red. That is completely wrong. In fact, the exact opposite is true. You should wait till the light turns red. The cars whose light just turned green have to yield to any cars still in the intersection; they cannot just drive forward and run into them. The safe thing to do when making a left turn is to go forward and "occupy" the intersection, then wait for the lights to change; once you're sure that opposing traffic has all stopped for the red, then you go to complete your turn.

Now, even if your mom is primarily at fault, there could still be some fault on the other driver too. Maybe he was going too fast, maybe he should've seen your mom. In any event, his share likely won't be much more than 40%. The most important thing here is the color of the light.

Mr. Stone-Molloy is right. Drivers making a left turn must wait for oncoming traffic to clear or stop, no matter what, or they are at fault. Even if the light has turned red, if the left turning driver sees a car coming the other way is about to run the red light, the left turning driver will at least be partially at fault if they make their turn and cause an accident.

She will be found 'at fault', all left turners are. Sorry, no excuses accepted. She 'obviously' turned unsafely, she got hit. Turn it over to her insurance company. That's what you pay the premiums for. If she had none, then work out a reasonable settlement and be sure to get a full Release. If she can't do that herself, she needs to hire an attorney to make sure it is done right. Feel free to contact me if you need to do so.