Complex sentence: Her standing in for Spicer occurred during the dismissal of James Comey and the controversy following it, and her aggressive defense of the Trump Administration's actions led to some speculation that President Trump was considering promoting her to replace Spicer.
Split into simpler sentences: Her standing in for Spicer occurred during the dismissal of James Comey and the controversy following it. Her defense of the Trump Administration's actions led to some speculation that President Trump was considering promoting her to replace Spicer.