Just to let you all know the outcome of this saga, after the first response I got from the UKBA which asked for the exact wording on my step-daughter's visa and then the second response to confirm my wife's immigration status and give them the exact wording on her visa slip with regard to "Visa Type". Then after the third try where I laid out all of the visa dates, arrival dates and the visa types for both my wife and step-daughter, I finally got the answer I was hoping for, "She may include her daughter under the age of 18 for no additional fee if she is applying as her dependant. But if she applies separately, she must pay the prescribed fee"
Iain.