Navigate to the websites of the sources that were cited by the student and check to see if she plagiarized any content from those websites. Be wary of any websites that are broken or that don't relate to the content the student produces; this could be a sign of web plagiarism.
Navigate to an online search engine and search for a few different phrases from a section of the work that you suspect is plagiarized. Search for those sections of a paper that don't use a style consistent with the rest of the paper or are too stylistically advanced for the student.
Use an online plagiarism checker such as plagiarismchecker.com, dustball.com or articlechecker.com. These websites allow you to search for duplicate content within an entire paper.