Although maternal sense of competence is thought to be a multifaceted construct not enough is known about the factors predicting it. We aimed to measure the mediating role of postpartum psychopathology (depression and childbirth PTSD) on the association between insecure (anxious and avoidant) adult attachment styles and maternal sense of competence. Further, we measured the moderating effect of mother-infant rooming-in practices on these associations. The sample included 268 postpartum women (122 (45%) fully rooming-in) who gave birth at a large tertiary health center and were followed as part of a large longitudinal study. Participants responded to questionnaires at 1–4 days postpartum in-person (a demographic questionnaire and the Experiences in Close Relationships Scale [ECR]), at two months using online questionnaires (Edinburgh Postnatal Depression Scale [(EPDS], Birth Trauma Scale (BiTS) and Parental Sense of Competence [PSOC]). Obstetric data was obtained from medical files. Significant direct links were found between insecure adult attachment styles (anxious: B = −0.15, p = 0.0016, and avoidant: B = −0.14, p = 0.0085) and PSOC, while rooming-in mode did not moderate these links. However, for both insecure adult attachment styles (anxious and avoidant) the indirect links through childbirth PTSD general symptoms (anxious: B = −0.05, 95% CI = [−0.11, −0.01], avoidant: B = −0.10, 95% CI = [−0.18, −0.04]) and PPD (anxious: B = −0.10, 95% CI = [−0.17, −0.04], avoidant: B = −0.06, 95% CI = [−0.12, −0.01]) were significant only for women who were in partial rooming-in. Full rooming-in with the baby in the first days may be a promising practice in attenuating the impact of insecure attachment styles on parental sense of competence, among women with some postpartum psychopathology.