In order to get the best idea of how the denman helps with curl definition and clumping, I would watch a youtube. (Just search denman brush definition curls.)
From what I understand, the hair goes against the rubber backing and the tension helps the formation of the curl. I have a really strong curl pattern on 99% of my hair, so the denman wouldn't really help me much though.
About your actual question: There's nothing particularly magical about a denman brush; it's just a tool for a different method of styling. It's not going to fix your limpness, or your daughter's frizz....
Just a side question: Why in the world are you using a pick? While there's nothing particularly "wrong" about this method, the way you asked your question implied that [the pick] isn't working...
Hair Type: 3c, Med-High Density, Low Porosity
CG since '09
Low Poo: KC Come Clean
Condish: AOHR, TN (Avocado), TJ Balancing Moisture
Leave in: GDL, KBB
Curl Lotion/Gel: CHS/CK
Others: CJ Curl Rehab, Jojoba Oil