Wisdom and knowledge are two very different things, and that's made very clear in The Truth About Forever. Jason has knowledge, and lots of it. But wisdom? That can only come from experience, and that's something that Delia has plenty of. Over the course of the novel, Macy comes to realize that she values wisdom over knowledge—and with all the craziness she experiences, we'd bet she's picked up a bit of her own, too.
Macy's mom is plenty wise, but since she doesn't listen to Macy, she can't apply it.
The Truth About Forever teaches us that suffering is necessary to gain wisdom.