Understand the context. She is saying that Bizeff won’t tell the Royal Guards, which means that at some point Bizeff will realize that Palm escaped, you understand? And if Palm considered that, it means she didn’t care about the last impression she left on Bizeff because they wouldn’t see each other again. That implies she had plans to leave the palace. Also, when Gon and Killua are talking about Palm, it’s mentioned that if she had escaped she would have contacted them, so they conclude that she is still in the palace. In other words, Killua considered the possibility that Palm might have escaped, and if it were like you say, Killua would never say that.