It is not recommended to give over-the-counter cough and cold drops to a 6-month-old baby. Medications containing decongestants and antihistamines can cause serious side effects in infants under two years of age. Instead, you can help soothe her cough and congestion by using saline nasal drops to loosen mucus and a bulb syringe to gently clear her nose. Ensure she stays well-hydrated with breast milk or formula, and consider using a cool-mist humidifier in her room. Please consult your pediatrician for a proper evaluation to determine the safest treatment for your baby girl.