Nana had been educated to serve others; that was the sad fate of orphans adopted by the church, people like Cecilia being the few exceptions to the rule.
Sure, this was better than starving or freezing to death on the streets, but a life of servitude was still far from satisfying. One of the few consolations Nana had was that at least she didn't have to serve the old perverts of the church who would no doubt abuse her given the opportunity.
In any case, serving others was what Nana had done all her life, so her current situation was utterly foreign to someone like her.
Desmond tended to make some tea to relax as a matter of habit, so he had brought along a tea set and some of Sasha's unique herbal blends.
Trying to get rid of the bad taste in his mouth from the previous massacre, Desmond prepared the tea without delay, and this being something quite natural for him; Desmond also poured a cup for Nana as a courtesy.