Oh, I didn't understand this while reading the novel, but the rating cards at the end might actually be a small Jing Xiu plot to test Ji Youyan's attitude towards her. She anticipates that from her comments she'd be expected to hold up a D, which under normal circumstances would make her the one bad rating and kinda stand out as scary and possibly incur wrath from the producers. So if Youyan was selfish, she'd stick with a C to leave all negativity on Jing Xiu but the fact that she also holds up a D and then quickly switches it around shows to Jing Xiu that she was trying to take some heat of her and help her out, which is why Jing Xiu is smiling to herself after the ratings are given.
Might be overinterpreting, dunno