Bulk email

I teach a vocation course. It is like a back to work program (welfare to work). My students have either never had a job or do not know how to get a job. Regardless of what I teach and the examples I provide in real world scenarios I always get the same behavior from the bulk of the lot. Class starts at 9 AM and ends at 3 PM. Many swagger in at 10 AM, 10:30 AM, sometimes 1 PM. During class many surf the Internet because they do not have computers at home.
That is a bit of background. One student on one occasion told me, “Why is you botherin’ me?” when she was not doing assigned work. We discussed her behavior that day and it got better but only temporarily. This was not her first snap back. today as class is being held she is in another room working on her resume. This same student sent me an email today while in the other room asking me for a reference. How do I say, “No” without dampening her spirits but showing her that she really needs to make some improvements?