This seems a bit tricky, Selda, and you're right to be cautious. I don't know the prose poem by Kincaid, but I can only imagine that the whole approach is fundamentally different, in technical/literary terms, to 'The Bell Jar'. This could possibly be useful ... but only if the style/approach of each had some direct relevance to the research question. I presume that the research question must have something to do with the themes & message of each work - since what else would two such radically different genres have in common? Does each work have something distinctive to say about the protagonist? Or about human nature? Or what?
I think the IB would accept in principle the comparing/contrasting of two different genres ... but only if, in practice, there is some credible argument for doing so. I would require the student to (1) explain clearly what point she is trying to make, and then (2) produce a very clear and explicit research question addressing the point.
Все закончилось. Действительно закончилось. Теперь можно возвращаться домой. Кольцо на пальце и есть тот Грааль, который он искал. Беккер поднял руку к свету и вгляделся в выгравированные на золоте знаки.