It is not unusual for a claim to take two weeks (or more) to resolve. There could be several issues going on. For instance, you stated the other driver already hired an attorney. As an adjuster, once you become attorney represented (wether you are the insured or the claimant) the adjuster cannot directly discuss the claim with you. It may be possible that the other insurance company has to schedule a recorded statement with their insured and their insured's attorney. This can place a delay on the claim process.
Additionally, some police reports take 7-10 days before they are ready and many insurance companies order these reports via regular mail or through a service that solicits and collects the reports. Most of the time there is not enough information on the drivers exchange and the adjuster has to wait for the full report.
There could be a coverage issue. Perhaps the other driver failed to pay her premium on time and there is a lapse in coverage or the vehicle she was driving was not on her policy. Remember, just because someone shows an insurance card at the scene does not mean they are insured.
When an adjuster is investigating a claim they need their drivers statement, in this case, your sons statements, estimates of both vehicles, police report and any witness statements. It may be that the adjuster does not have enough information to finalize liability.
Additionally, your carrier has a fiduciary duty to stand by your facts of loss unless the evidence states otherwise (ie citation, witness, veh/scene photos). If both your son and the other driver are claiming they had the green light and had right of way and there were no citations or witnesses they may decide to stand by their insured.
Here is my suggestion. Talk the the adjuster of the lady's insurance company. Ask if there is a coverage issue or if liability is still being investigated. Be helpful, if the adjuster still needs a copy of the police report then provide one. If the adjuster needs a statement from your son then have him provide it. You can only help yourself to keep the investigation moving forward. Remember claims are resolved fastest when there is cooperation from all parties. If the other driver is not cooperating it may be the reason there is a delay.
As for hiring an attorney, that is a personal choice. Just be sure to weigh the pros and cons. Communication is key, call the adjuster and if you can't get through call the adjusters supervisor. Make sure you understand why the claim is not resolved, it may be as simple as faxing over a police report to get you claim paid