There's a saying that you should keep in mind. "You can't teach a drowning man how to swim." What that means in this case is don't say the job is bad you need to get out of there (hard, I know). Don't say come over to work out (you guessed right). Instead you go to where she is. You call. You do the work of keeping her out and about. Keep a mental note of what she does and remind her that she has come a long way, by recounting accomplishments. Finally give her little assignments. Have her call each you each evening after work, to let you know how her day went. Since you know the work place give her assignments for there too--it might be to copy something from the bulletin board for you or to give a message to someone. Just little things, so she has something positive (doing a small favor for a friend) to think about during her day--you might even encourage silent or mental rebellion--things like wondering what someone looks like naked--again to get her to think about things that might put a smile on her face. And do things like you already did--have her meet you for lunch.
People make excuses for a couple of reasons--but generally fear of change is behind them. Tell her, "the smallest change is the best change." Get her thinking about small changes rather than big sweeping ones. That way she can find her own answers and get up the courage to follow through.
I hope this helps and good luck,