Parental reflective functioning—the tendency to consider children's mental experiences—is associated with sensitive parenting. Maltreating mothers may have reflective functioning deficits given their risk for biased child-related cognitions and their difficulties with sensitive emotion socialization. It is therefore important to examine reflective functioning among such mothers and in relation to sensitive reminiscing about children's past emotional experiences. Furthermore, little is known about developmental trajectories of reflective functioning over time. Reflective functioning may be malleable following maltreating mothers' participation in Reminiscing and Emotion Training (RET; Valentino et al., 2019), a relational intervention aimed to enhance sensitive reminiscing. Moreover, longitudinal reflective functioning trajectories may be associated with patterns of change in sensitive reminiscing. The present study investigated reflective functioning and reminiscing longitudinally among mothers enrolled in a randomized controlled trial of RET. Participants included n = 81 maltreating mothers who received RET, n = 79 maltreating control mothers (CS group), and n = 82 nonmaltreating control mothers (NC group). Results provide evidence for the role of maternal pre-mentalization as a mechanism associated with difficulties in sensitive guidance during reminiscing. In addition, in comparison to mothers in the CS group, mothers in the RET group showed reduced post-intervention pre-mentalization and increases in interest and curiosity over one year. Finally, an indirect effect between RET and post-intervention sensitive guidance through post-intervention pre-mentalization was observed.