Hans, you need to get out of your head for a moment, go drink some beer, do something that's not related to her.
The facts are, there is no longer any wedding diversion to worry about, she is looking forward to meeting you, what's the problem? if she is 400km away from doing a webcam and you can't do it on your mac then forget about it, its a non runner, what's the point in thinking about it. You will know if she is for real when you meet her, my guess is that within the first few minutes you will know.
The translator charges are ridiculous, the price I was quoted in Guangzhou was 200RMB a day, plus of course the daily expenses such as food, bus rides etc. You will definitely be able to negotiate this, there will be plenty of college students etc only too willing to practise their English and spend the day with you and your lady. My suggestion is when you meet her ask he if she can find a translator, heck write it in an email to her i bet the translator will suddenly offer a better price if they see themselves loosing the business.
If the worst comes to the worst, the agency will only be too happy to introduce you to someone else. Don't forget the girl is probably paying you a least the equivalent of a months wages (and quite likely several months wages) for her to meet you to the agency, if thats not showing committal to you than I don't know what is.