Skye wasn't sure how to process what Magnus had just told her. To be honest; she wasn't even sure that she and Shasta actually got along. Drunk and sober were two completely different states of mind. Skye'd seen plenty of people who's decisions and judgement were compromised by alcohol.
Their joint performance during the victor's banquet wasn't the only reason Magnus thought the two were friends. Shasta had seemed friendly to the princess during dinner the night before the trials. When the trials were going on, Shasta had rested her arm on Skye's shoulder as they'd talked. Anyone else watching would've come to the same conclusion: that the princess and the VC were friends.
The king was beaming like he'd done Skye a huge favor. She smiled back, but it was completely fake. Magnus knew her well enough to tell that she wasn't thrilled with his order. There were others he could've assigned, but Shasta truly was the best fit for her.