My 2 year old was constipated pretty badly. she finally passed a very large bowel movement but she is still in pain. could it be anal fissures or something else?

That symptom can happen when the child had been constipated and then passed out hard stool which can irritate the ano-rectal mucosa. You can put her on warm sitz bath for a couple times in the next 24 hours and apply K-jelly ointment or Lidocaine cream 4% (OTC) on the anal canal and perianal area after each sitz bath. Your child needs to drink fluid well and eating more foods with fiber.