"Investigations not thorough enough"

I won't go into full details. My Mother was in Antrim A&E and was told she had a kidney infection that was not bad enough for an antibiotic and my mother was sent home with anti-sickness medication.

At home my mother showed no signs of improvement and the medication had no effect.

We then decided to phone an ambulance and my mum was taken to another hospital and the care she received was excellent and my mother received the correct diagnosis and needed surgery for a small bowel obstruction. 

I do not understand how something like this could have been missed at Antrim Area Hospital A&E department.