My suggestion to anyone struggling with rhythm is to work on Bartok's For Children, of which there are two volumes. In these pieces he indicates all types of rhythmic order, some metric, some not. Learning the meaning of the various signs can do a lot to make the student aware of the difference between metronomic regularity and other ways of getting from one bar to the next, or from one beat to the next. Becoming aware of one's power to control this element is the key to fixing the problem.