Caleb wees more after the first feed in the morning that he does all night. I sleep him with both boosters and he is never wringing wet even if he sleeps 12 hours. I change him and use the same combination of two boosters and he is soaking at his next change. He usually gets quite grizzly if he's really wet though it is better for him if I use a fleece liner.
If you're getting up to her for a feed than you can change her then to see how her wetting pattern is.
I've never been able to have a disposable on any of my boys for as long as 4 hours without them getting a rash so I don't know any different IRT frequency of changes.