Take a look at the sentence again:
Jackie always made it a point to sit in the front row because she liked
to focus on the lecture and take good notes, the excessive spitting of her
Latin professor, however, drove her to the
back of the room.
The comma between professor and however is legal in writing. The excessive spitting of her Latin professor drove her to the back of the room is a main clause. However is interrupting the flow of the clause, so this conjunctive adverb requires a comma both in front and behind.
Go back to the sentence to try again.