It would depend in part on how humid the air is where you live. If you live in a desert climate, a humidifier might help give some relief assuming you can prevent it from causing a mold problem. If you live an in already damp climate, it probably won't help all that much.
I don't own a humidifier and haven't for many years. I have had bad experiences with stuff growing in them and did use one very regularly for a long time prior to my diagnosis. I would think your daughter might benefit from irrigating her sinuses if she will tolerate that. I also have found that washing throw rugs, curtains....etc....can stop someone from having a sniffly, stuffy nose and it's good for the whole family. Everyone breathes better. (I found this helped so much that I ultimately got rid of throw rugs...and a whole lot of other things.)
Good luck with this.