For your 13-month-old daughter's dry scalp, it would be best to use a gentle baby shampoo that is labeled as "tear-free." Washing her hair for about 10-15 minutes each day is recommended. Ensure to rinse thoroughly to prevent worsening of dandruff. If the issue persists or gets worse, consider using baby oil before brushing out any flakes. If the problem continues after around 4 weeks, it would be advisable to consult a pediatrician.