My daughter randomly hiccups once loudly at least a couple times a day. is there a reason for this? she is 20 but has been doing this most of her life.

There is a reason.: But if it hasn't been found in many years, it may never be found. Either her vagus nerve is being irritated along its course through the gut, chest and neck ( i suspect that is the cause) or she has dysfunction in the brain hiccuping areas ( hypothalamus, medulla oblongata, reticular formation of the brainstem). She deserves a good exam to exclude obvious causes and consider imaging.