Hello. Read this. Or don't, I don't care.
A friend is having trouble keeping up with the class. You suspect
that bad study habits may be causing her grades to drop.
A way to solve this problem would be simply to talk to her, explain to her that she has to take school seriously and make it her top priority. If this didn't work, you could think hard about what she regularly likes to do in the place of studying or homework, and help her focus on her work rather than whatever else she wants to do. If you did this enough and pounded the point in deep enough, she might start to understand what she has to do, and eventually do it on her own to keep up with class.