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she took the law into her own hands by grabbing my and slamming me against a news paper stand
I think you should report this to the manager of the station. Give them the time of the incident and where it took place; they should have the name of the employee.
You were wrong to shout at her, but you were shaken after getting caught in the gates and she got in your face and you lost your temper. It wasn't the best way to handle the situation, but a lot of people would have done the same. The spitting was out of line; technically you have assaulted her, but she had absolutely no right to use physical restraint.
To avoid things like this in future, if you have already gotten through to the other side, ignore her and just walk off. Leave this woman to huff and puff if she likes, you haven't done anything wrong. Don't rise to people like this; they like to kid themselves they have more power than they really do.
If you are still stuck on the wrong side, be very calm and speak clearly and slowly. Don't shout, and definitely never spit.
edit; whilst I think reporting the incident may be a good idea, I wouldn't recommend trying to press charges; they may counter sue you for the spitting or throw the case out.