Benner would be an appropriate fit if the 'challenges' to which you referring are clinical in nature, however cultural differences between the clinical and academic environments also exist - if you are referring to students 'adjustment' in another setting then a different theoretical basis may be warranted. Good luck with your work.
A very interesting study indeed. I am even considering doing a similar study in the area because the focus is always outward looking. We are concerned with the receipients of our care (it is good to do) and leave little room to focus on ourselves as educators, providers and our trainees.
If there have not been any previous studies of the challenges of nursing students in Ghanaian schools, you might want to start with a qualitative study. A Phenomenological approach would work nicely asking about their experiences. Benner based a lot of her work on the Dreyfus Model of skill acquisition. Both would fit a quantitative approach for your study.
The theoretical framework is one of the most important aspects of your research study. It serves as a guide on which to build and support your study.
You did not state whether you are doing a qualitative or quantitative study. The framework should guide your choice of design and data analysis. What is your research question? Design? For example, I am performing a phenomenological study into the experiences and perceptions of psychiatric nurses who work with psychiatric patients diagnosed with a chronic pain disorder. Peplau's Interpersonal Relations theory is my framework, because it focuses on the nurse-patient relationship. Look at what you are trying to answer (research question) and how you plan on guiding your study. This will help narrow down your choice of theoretical frameworks.