Oops, you caught me out. I started trying to figure out why she hadn't gone, and had a big conspiracy type thing in mind, but you (yes, it's your fault) suggested she had to stay home and 'look out for the kid'. Then I kept getting this image of her standing in front of her kid with a pike, and well, the rest just happened. So no, I have no idea why she didn't go, but with any luck it'll come to me.
Did you think that John sounded odd in Lost Tales when he told the reporter Delenn wouldn't be there? It was a weird inflection in his voice. He sounded pretty normal when he mentioned her at the end, after he'd talked to her. Maybe they had a rip-roaring fight before he left? And then made it up when he talked to her on the way?