Rear Ended by drunk driver

2 Days ago was rear ended by a woman, I was doing 45 in a construction zone on a freeway in St Louis, she hit me hard enough to total my car (approx value $15,000.00). She said she was on the phone and she failed the roadside sobriety test, was taken away in the police car. I went to the emergency room and no broken bones were found but I assume soft tissue damage occured as noted in other posts. Initial recomendation and treatment: Muscle relaxers, pain pills, rest, and to see my primary care physician next week. My neck and my back are very sore and stiff. Even with the seatbelt on I was thrown forward and back hard enough to break my seat leaving it permanently reclined. One of the things one of her insurance adjustors said is I have whiplash (obviously) and that the pain will only get worse over the next few days (so far everyone has said that, ie. the emergency room and coworkers who have experienced this).Another of her insurance adjusters said the injury claim can be settled at any time, now amonth from now, and so on. Typically he said they pay the emergency room, rental car, Doctor visits and treatment, lost time from work, and then typically $500.00 for pain and suffering. From what I see on this site it sounds like I should not settle until treatment is complete and it sounds like the pain and suffering is a very lowball offer?