At the beginning of an assignment, I think it would be advisable to ask the supervising MD how they give feedback and how they would prefer you to interrelate. For example, when the feedback was given "you tried hard" it would be nice to know if you should follow up at that moment or is there another time where you could ask for/receive feedback. For example, when she said that, you could have asked for constructive feedback then or asked her for time to review at X time in the future, such as in her office later or over coffee or whatever time she had previously indicated would be good to receive feedback.
Part of a supervising physician's job is to give feedback and getting "you try hard" isn't going to help you do better in the future and, like most students, getting better is the goal. I'm sure not many students are ever perfect in their rotations, so it's not like you are asking for anything out of the ordinary. I would also advise sitting down and formulating questions to ask her at these meetings to tease out (if needed) the nuances of what she has observed and what needs to be improved or amplified in regards to your performance. Ain't none of us perfect all the time.