Well, you will probably find lots of differing opinion on this but here is mine:
If your daughter turns ten before you arrive, she should be on the adult plan (although Disney will probably not enforce this, if she is officially listed as 9 on the reservation).
If you daughter turns ten while in WDW, I think it is fine that she is on the child's plan. (Once again, you will not be "forced" to put you daughter on the adult plan the day she turns ten, Disney would only go by the age of your daughter listed on your reservation at the time you made it).