This is something she should talk to her professors about. Even if you were experienced in a specific STEM field, it would be hard for you to help her, as it's going to vary hugely by the subfield, her experience and knowledge, whether she's working in a lab, and dozens of other factors. She should be wary of fake journals, which will often publish anything but require payment. Again, her professors should be able to help.
And to be blunt: If her research is not enough to get the attention of a professor at her school, it's not publishable. If she doesn't have a specific paper that she wants to publish but just generally wants to publish, then she's also not ready. (It would be sort of like saying, "I want to go to the Olympics" without having chosen a sport.) As a student, focus on the substance and follow your interest, and (maybe) the publications will come.
There are some journals that are targeted at undergrads:
https://uncw.edu/honors/info/student-life/journals-that-publish-undergraduate-student-research.html