Review the item:
Davina, a good friend from my biology class, prefers what is under a guy's
skin to what is under his clothes, for this
reason,
she is pursuing a degree in radiography.
The comma between reason and she is perfectly legal. For this reason is a prepositional phrase that is introducing the main clause that follows: she is pursuing a degree in radiography.
When a prepositional phrase acts like an introductory transition, as it does in the sentence above, use a comma after it.