S.W.
I work in Outplacement, helping people get jobs. Real work experience is very valuable these days, even if the job is "assistant". If she can manage the job and school, she will be way ahead of someone who gets the same degree and waited tables or something throughout school. Good luck to her!
One piece of advice I've heard about starting working a low level position in an office. Read everything you have access to. Read and listen and learn.
And personal contacts can be as or even more important than completing a degree in a tough job market. There are a lot of people graduating with degrees that can't land a job, because they don't know how to network. 75 - 80% of professional jobs are obtained through a personal connection.
Added: if she proves herself to be a valuable employee, the firm might let her arrange her schedule around a class here and there. It's been done.