Final answer:
Shellie was most likely given an anticholinergic medication to treat her Irritable Bowel Syndrome, which can lead to dry mouth as a side effect.
Step-by-step explanation:
The medication that Shellie was most likely given to treat Irritable Bowel Syndrome is an anticholinergic medication. Anticholinergic medications work by blocking the action of a neurotransmitter called acetylcholine, which is responsible for stimulating saliva production. By blocking this action, the medication can cause dry mouth as a side effect.
Learn more about Anticholinergic medications