Minor car accident and not added in the insurance, what to do?

• driving school insurance
• stop limit order
• tax write offs

My fiance recently crashed into someone. He drove his dad's pick up to the mall and on his way back he crashed into a lady. She drove way 1 lane way (1 going 1 coming) she stopped to turn into her house and my fiance bumped into her going less than 30 m.p.h. & the speed limit was 40 m.p.h. it was also raining and it was windy & the tree branches were hitting the wind shield. They exchanged information & there was no police report but she was going to call the insurance. Her car's side mirror broke, the bumper dent a little & the back light broke. Now the insurance called my in law to tell her they were going to sue my fiance because the lady went to the doctor's to get checked & i think something came up. But my fiance said she looked fine when they were exchanging their info. Thing is he is not under his mom's insurance, what can we do? Whats next? We are willing to pay for the damage in her car & hospital bill. Is there a need to go through a lawsuit?

Minor car accident and not added in the insurance, what to do?