Complex sentence: The red kryptonite causes Kara to develop a more confident and abrasive attitude, leading her to wear new, more stylish outfits and upstage Siobhan when Cat asks for a list of replacements for Lucy at work.
Split into simpler sentences: The red kryptonite causes Kara to develop a more confident and abrasive attitude, leading her to wear new, more stylish outfits. Kara then upstaging Siobhan when Cat asks for a list of replacements for Lucy at work.