Hi, I'm planning on applying to a Master's Program in General Psychology and have 2 possible letters of recommendation from professors but I am struggling to come up with a third. While I'm aware that professors hold more sway over admissions than supervisors, I have a sort-of dilemma on my hands: I was assigned an independent research project my junior year with one professor for a semester, but he was a very busy "superstar" professor who frequently forgot my name and canceled meetings with me. Although I received high marks on the project, we met a total 3 times over the semester. Add that to the fact that it has been 2 years since the project and I took a year off after school, and I have some doubts he remembers who I am and what my project was about. While I doubt he'd refuse to write me an LOR, I have less faith in his ability to write me a good, personalized LOR.
On the other hand, I also worked as a research assistant for a year in another professor's laboratory as an undergrad, with a Ph.D candidate as my supervisor. She's very familiar with my particular strengths as a researcher and acknowledged my contributions in her articles published in the Journal of Social and Behavioral Psychology, and has demonstrated a willingness to act as a reference. However, she is still a Ph.D candidate, not a professor, so I am not sure if that would look bad on my grad school application.
Any suggestions?