I inferred you are referring to Violet instead.
Answer:
she chews "Gobstoppers" which are not meant for chewing.
Explanation:
Remember, it all started when Violet entered the inventing room and she began to show an interest in gobstoppers, believing them to be similar to gum, even though they were not meant for chewing.
After ignoring the warning from Wonka, she begins chewing the gum which leads her body to swell.
