Here is the item again:
Jackie always sat 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 notes and the creates a comma splice. At this spot, there are two complete sentences joined with a comma alone, making a major sentence error. Jackie always sat in the front row ... begins the first complete sentence. The excessive spitting of her Latin professor, however, drove her to the back of the room is the next complete sentence.
To fix this problem, you could put a period after notes and capitalize the T for the.