Complex sentence: She was replaced by Jacquie O'Sullivan who stayed with the group for three years, and they had UK Top 10 hits with "I Want You Back" (1988) and "Help!" (1989).
Split into simpler sentences: She was replaced by Jacquie O'Sullivan, who stayed with the group for three years. This line-up had UK Top 10 hits with "I Want You Back" (1988) and "Help!" (1989).