You want to activate the new *Moto G4 Plus *as an upgrade/replacement for your existing Moto E device (current line of service). This will automatically transfer your current phone number to the new Moto G4 Plus.
Once completed, and you have moved/backed-up any data you care to retain to the new phone, you can FDR (Factory Data Reset) the Moto E and reactivate a new line for your daughter on your account, or she can activate the Moto E on her own account.
Detailed instructions can be found here: Activate My Phone
Feel free to ask any and all questions you have or if you would like additional assistance.