From my experience evening classes are good, but some people require to be in the country and ‘immersed’ in the language for it to work.
I came to switzerland (french part) with 1yr of french evening classes, but i couldnt speak or write for jack.. i’d quit my job in london and enrolled myself in a 3month 25h/week course.
That did the trick and i then got a job 2 months later..
If she has transferable skills she’ll get a job easily – with proper english and up and coming german she should be an interesting catch for german companies..
edit: What i wouldnt do however, is to stay around and chat to english speaking people in the beginning.. good to have new friends etc, but not good to hold onto the language. if her head works in any way similar to mine (crap with languages) then she’ll need to free up space to take on the german.. and dont just sit around watching english tv..
edit again..: my gf at the time, now wife, didnt really give me an enormous advantage tbh.. the 1st 2 months i couldnt communicate in french..so we spoke in english. but as soon as it’d clicked we spoke in french..