I had this done... they pulled 4 baby teeth and 4 adult teeth, then later I had to have an expanding retainer.... I was about her age.
I remember it being quite painful and difficult, but then again, I had 8 very sensitive holes in my mouth. The thing that made me most upset, is that I went to have the surgery to have my adenoids and 2 teeth removed, and when I woke up, I had 8 removed. Not very happy that I was not told the truth. So, I would simply explain the procedure, tell her how you will all help her heal and what she will have to do and eat, and explain how it will benefit her.
Now a days, it is more common to expand the mouth for new teeth, instead of pulling them. Have you thought about getting a second opinion?
I'm saying this part due to what GammaG said about the children getting braces at 7 and 8. Braces that young is a waste of time and money, and undue discomfort for the child, since teeth will reset, and the child will needlessly be in braces for many, many years. It's best to wait to do braces when they are preteens or early teen years, according to my pediatric dentist and my friends who are also dentists.