Complex sentence: Kellie completed her purchase, left the store, and met up with Brianna in the parking lot, but as she drove her to Jillian's home, Brianna seemed shaken and agitated.
Split into simpler sentences: Kellie completed her purchase, left the store, and met up with Brianna in the parking lot. As she drove Brianna to Jillian's home, Brianna seemed shaken and agitated.