Complex sentence: From the age of 14, she performed with various bands, including a blues rock band called Kashiro, before joining with Robert Westerholt in 1996 to form a band called The Portal, though the name was changed to Within Temptation before their debut recording.
Split into simpler sentences: From the age of 14, she performed with various bands, including a blues rock band called Kashiro. As their partnership grew, in 1996 they came to form a band called The Portal, though the name was changed to Within Temptation before their debut recording.