it seems that your sister is having acute gastro-enteritis
giving rise to this problem.
continue with lomotil.
Give her antispasmodic tablet like Dicyclomine
Give her Ofloxacilin, tindazole combination tablet for 3 days.
Give plenty of water and electrolytes to prevent dehydration
Give her light diet like curd, rice, buttermilk, coffee etc.
Ok and take care.