Background: Urinary tract infections (UTIs) represent a significant public health concern, particularly in children with structural abnormalities such as vesicoureteric reflux. Prolonged antibiotic exposure in these patients often contributes to the emergence of multidrug-resistant organisms and restricts therapeutic options. Probiotics have emerged as a potential adjuvant strategy to reduce infection recurrence. Case Presentation: A female infant born at term (38.6 weeks), with a prenatal diagnosis of bilateral hydronephrosis, experienced recurrent UTIs from the neonatal period despite both prophylactic and therapeutic antibiotic regimens. Serial urine cultures revealed infections caused by extended-spectrum beta-lactamase (ESBL)-producing E. coli and K. pneumoniae. Methods: The isolated strains were evaluated in vitro against Lactiplantibacillus sp. LH01, a probiotic strain derived from human milk. Following confirmation of its antimicrobial activity, an individualised intervention was initiated: daily oral administration of 1 mL of the probiotic (10⁹ CFU/mL) for one month, under medical supervision and without concurrent antibiotic therapy. Results: The probiotic demonstrated 89% inhibition efficiency against multidrug-resistant strains, accompanied by a notable reduction in UTIs frequency. Follow-up cultures showed reduced pathogen growth and a loss of the ESBL phenotype, facilitating clinical management and allowing previously contraindicated surgical interventions. Conclusions: Lactiplantibacillus sp. LH01 proved a safe and effective adjuvant in managing recurrent, resistant UTIs in a paediatric patient, highlighting the promise of probiotic therapies.