Lady Parthia could guess why Lady Miranda told the white lie about the number.
So realizing it, the lady too decided to keep up the act, one because Lady Miranda and they were right now allies and it would be not polite to poke holes in the other party's credibility, but much more so because she was not willing to shatter the hopes of the man sitting next to her.
Alexander really looked like he could really use this good news, even if it was not true.
Thus Lady Parthia too played her part in letting Alexander enjoy the brief respite and allowing him to immerse in the thought that his situation was about to imminently improve and by a scale of two at that, thinking that young man could deal with the disappointment later.
Although such tender consideration did not really help Alexander that much as Lady Miranda was quick to inform him of some other dire news, shattering his gleeful, relieved state.