My daughter has hirschsprung disease. How will this affect her?

Depends. Most children treated surgically for hirschsprung's will do well and live a normal life. A lot depends on the length of colon/intestine involved.
Variable. There is a wide variability in the severity of hirschprung's disease. Some cases are picked up early in infancy and require a surgical repair, while others are much milder and aren't diagnosed until adulthood. Generally, if the diagnosis has been established, surgical repair is the best option in order to prevent future problems with stool production, constipation, and intestinal stretching.
Probably not much. Following completion of corrective surgery, other than some lower bowel or evacuation problems, often not bad, most people do well. Assuming no other non hirschprung problems.

Related Questions

Please can you advise me what to do and what are the treatment for hirschsprung disease because my daughter is very ill and we are from iraq?

Treatment=surgery. The basic treatment of hirschprung disease is surgical. If a high lesion, a the upper bowel is brought to the skin of the abdomen and an opening created so poo can exit. Later, if possible, this can be relocated to the normal position and reattached to the lower bowel after the blocked area is removed.
Go to hospital. Your child has an area of their intestine that is not contracting properly. This can cause severe constipation. There may need to be a surgery to relive this area of the intestines. A pediatric surgeon would be the best person to see. An emergency room can also help you get into see a surgeon if you cannot find one on your own. Good luck.
Irrigations. If your child is very ill, irrigations with saline in small volumes in and out which can decompress the colon and bypass the obstruction. This is a temporizing measure. If she is sick, she needs attention. Someone diagnosed hd and should refer you to a pediatric surgeon for care.