Complex sentence: According to Hill, during her two years of employment as Thomas' assistant, Thomas asked her out socially many times, which she declined because she felt it would be ill-advised to have a social relationship with her supervisor.
Split into simpler sentences: According to Hill, during her two years of employment as Thomas' assistant, Thomas asked her out socially many times. She declined these invitations because she felt it would be ill-advised to have a social relationship with her supervisor.