The main point you want to make regarding the mother-daughter relationship in Romeo and Juliet, particularly Juliet, is to defend the argument that society has taught her and her mother to relate to one another as they do. The Capulet's are aristocrats. Both Juliet and her mother are obliged to follow rules of their time. Those expectations include, for instance, Juliet having a nurse (or governess) to take care of her, from breastfeeding her as a baby, all the way to counseling her in her older years.
For your thesis statement you could write about the following:
No mother could possibly replace a woman who has given a child every single emotional, physical, and psychological need, especially after the children become adults and go back to those whom they needed the most during their growth.
We can definitely see that Lady Capulet does not interact enough with Juliet to even begin to understand her. Her nurse, however, does In fact, she is the conduit for Romeo. Hence, it is not so much that the mother/daughter relationship is strained, but mostly that the mother/daughter relationship has a rule of engagement that must be followed, and which ends up ruining the relationship altogether.