Complex sentence: Lina's first performance as a stand-up comedian was while still at St. Andrews University in 1998, but she didn't perform regularly until she moved to London in 2000 to do her PhD.
Split into simpler sentences: Lina's first performance as a stand-up comedian was while still at St. Andrews University in 1998. She did not perform regularly until she moved to London in 2000 to do her PhD.