Diligent study means to make up for the deficiency or defect in study through hard study, diligent study and remedial study. From the context of the sentence, the primary school math teacher said that your daughter "can make up her studies diligently", which means that your daughter may have some shortcomings or needs to be improved in math learning, but through hard work, diligent study and counseling, these shortcomings can be made up and the level of math learning can be improved. This may be the teacher's affirmation and encouragement of your daughter's learning attitude and efforts.