How do I complain to chair if my advisor regularly writes to scam journals to get tenure?
Your relationship with your advisor is extremely important for you getting a PhD. I would only contact the chair if you are absolutely certain that you would be able to find a new advisor if things went bad between you and your current advisor. When her tenure comes up for review, someone on the panel will know that these are scam journals. The fact that the chair has already denied one of her expenses means there is likely a red flag in her file (metaphorically). Now if she forces you to publish in one of these journals, you should absolutely complain, but don't complain about what she is doing with other students unless you think it is worth losing your advisor completely and creating enemies in the department. You can talk to the student who actually was going to go to the conference suggest he complains, but ultimately I think that is his responsibility. So again, refer to the first point; make sure you have an escape plan so to speak, and make sure that you are OK with potentially not earning your PhD because you stood up for yourself.