Yes, she still needs to fill this form by providing the information of herself, her souse (you) and her parents. Section B would be "N/A" for her if seh doesn't have any children, but make sure to write N/A is all blanks and sign and date where it says that the principal applicant does not have any children. And then in Section C she needs to provide information about her siblings. So even if they won't be accompanying her, this is the only form where she would still provide all the information.
Hope this helps !
Good Luck