First thing first, you need to understand what she claimed and what charges she brought about. You need to talk to the lawyer to get a copy of the claim and discuss a possible answer.
Check the statute of limitation in your state. Normally states set a two year statute of limitation for car accident recovery. Based on what you said, the accident happened two and half years ago, this should run out of the statute of limitation already and should be a non-case, unless there is some intervening cause to run the statute anew.
If this accident is still within statute of limitation, you need to check the the police report to see whose fault that was. If it was 50-50, some states bar recovery of the plaintiff.
If the report did not specify, then there is a little job to do. Most states treat accident case under negligence per se. This doctrine requires that your state criminal statute was designed to punish negligence as such, the harm she suffered was the harm the statute specified, and she is the type of persons the statute designed to protect. Under the circumstances it is not difficult to establish negligence per se. Even she could establish negligence per se, it does not necessarily follow that she could win that case. She has to prove causation. Causation includes cause in fact and proximate cause. To prove cause in fact, she has to claim that the car accident was the substantial factor to her back pain. This you need to talk to the lawyer again to find out what kind of evidence she has. What kind of job she does. For example, if she is a cashier, being standing most of the time, she could develop the same syndrome and she really can not claim the back pain was due to the car accident. Maybe she had another accident, fell from somewhere… You got my point here. Unless she has a direct doctor examination right after the accident it was already hurt two years ago, she could not prove that. Which, I really doubt, since, if that was the case, she could have sued two years ago. The proximate was also very difficult to prove. Again, she has to have expert opinion that the back pain was foreseeable.