Yoshigahara was observing the approaching man, obviously it was something she wanted, social interaction, instead of just sitting and and guarding the party. Her expression however remained careless as the Hacker found his place beside her, his question however could be answered in so many ways, but this time she wanted to be herself.
"Question is how much do you trust me? What if I would say it's just a glass of water? She definitely wanted to see if he believes her words or will stand ready with typical Hacker behaviour.