Violet Beauregarde is a character in Charlie and the Chocolate Factory who swelled after eating blueberry gum. What is causing Lisa’s body to swell?

I inferred you are referring to Violet instead.

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.

igneous rocks which formed by the crystallization of magma at the surface of the earth called extrusive rocks. they are characterized by fine-grained textures because the rapid cooling at or near the surface did not provide enough time for large crystals to grow.