See the article Remove family members from a Family Sharing group on Mac - Apple Support
As the family organiser, you can remove members from the Family Sharing group. After you remove someone from the family group, that person may be able to join or set up another family group. However, each person may only join two family groups per year. (Rejoining a family group or creating a new one counts against this limit.)
Children under 13 can’t be removed from a family group (age varies by country or region). However, you can move a child to another group using Family Sharing.
Second method you as family organiser can disband the group , she can create her new family sharing account ( as now she is above age 13 ) Set up Family Sharing - Apple Support