Could you take her to your preferred orthodontist for an consult? There is not charge for the consult (including xrays), at least where we go. Well respected practice.
I would venture to say that the preference is probably dictated by WHY the procedure is needed. Our daughter had 4 teeth pulled this summer, per recommendation by her ortho. She has lost very few baby teeth, and has 4 permanent ones that are/were not turned upwards beneath the baby teeth. So,their roots were not being resorbed and hence no loose teeth. In addition, they were beginning to push against the roots of the permanent teeth she DOES have, next to them. Which could severely damage the roots of those teeth.
All of this was shown to us on xrays and explained by the ortho. She had 4 pulled and we are waiting, hoping, that the new teeth turn and come up in the now open spaces (path of least resistance and all that...).
Rather than speculate, why not go get a 2nd opinion from an ortho? After he tells you his/her recommendation, ask what he thinks of extraction, and why your daughter's dentist might have suggested doing that in stead.
Remember too, an extraction by the dentist pays the dentist. An expander by the ortho pays the ortho. (Just to be realistic, it helps to remember these things). In our case, the ortho recommended work that they don't do, it would be done by the dentist. Our daughter will eventually be an ortho patient for her overbite. But that is some time in the future when she gets her permanent teeth. (Still waiting...lol)
But get explanations as to WHY one treatment option is better than the other. Don't just accept the recommendation without the underlying basis for it being the better option.