ellceeelll, im sorry you are going through this. I have an 18 year old who had counselling when she was at school, although it never really amounted to much.
Has your DD only been like this since the accident or has the accident brought it all to a head?
I can't really offer advice as i dont think i ever really got it right with DD. But as someone who is on citalopram herself, i didn't want lots of sympathy or pity, i just wanted to know that someone was THERE for me. If that makes any sense.
Where does she work? Does she like her job? could it be time for a change? I have had to learn a very hard and painful lesson with DD and that is totally step back, it is awful, i hate it, i feel like a bad parent, but she is happier for it. Not working at the moment and being a lazy arse about looking for another job. I just hope she comes round in her own time. Maybe she needs to take some time out from work etc...if she is only 18 then it sounds like she has gone from school straight to work or after college - might need a "gap year" or something to sort out where she is going in life.
I would say, just be very watchful of her over the next few weeks because the side effects of citalopram can make some people feel worse in the first few weeks but this wears off. Make sure she knows this and that she MUST talk to you if she feels "weird" at all. But don't tread on eggshells, she is not well, she is not a freak, if you start treating her differently she is going to feel very conspicuous. I would make it clear you love her an will talk any time she wants to but dont push her into it. Mine just you to tell me what i wanted to hear anyway.
Good luck, this is a difficult time but it will get better.