She could elaborate. It'd be so easy to say she's too tired to keep going on like this, but that, at least, does feel like a little bit too much to say right in front of a child.

"I missed quite a bit of sleep when you and everyone else attempted to return home," she instead says. Which is also factually true. It was hard for anyone to sleep during the train's constant attempts to re-enter the void, and it certainly wasn't made any easier for Alice in particular due to her mind already being a mess, and even moreso due to the after effects of that.

It's why she's still feeling it now.