Is she tracking her ovulation?
Track ovulation, have sex every other day during ovulation and the day after ovulation, stay in bed for 15 min after climax with legs propped up. Could be a luteal phase defect, ask dr for progesterone. Certain foods upset the pH balance in women, try restricting diet in the days leading to ovulation. It may help if she climaxes first to help lubricate the area for better travel conditions for sperm meet to the egg (can't prove it but from experience this produces boys). Avoid other lubricants, douching, and anything else that would be inserted. Other than that your Dr is the best person to ask