They could have gotten the driver info from the license plate. There's several websites that will run plates for a fee. They can also locate her via phone number, which the lawyer could have obtained by FOIA requesting the 911 call. As callous as it may sound, she would've been better off just driving away without making that 911 call. Or make the call without incriminating herself.
I've actually asked lawyers about a situation similar to this that happened to someone I know and they said the fault would mostly or entirely lie with the car that swerved and lost control. She should be good but wouldn't surprise me if some unscrupulous lawyer sues her.

