You can change her number free of charge in self serve. Is she prepaid or postpaid?

It’s monthly so I guess post paid?

Yes, probably then in that case you can change her number once per billing cycle, so pick a nice one

Edit: I meant to add that on postpaid you can also enable call control, to keep at least robocalls out.

Thank you. But how do I change it? Do I have to go in person or can I do it online?

You will need to do it online, in self serve. Do you have access to that?

Here are the steps to change your number : 

1. Log in to your Self Serve account.
2. From the Self Serve drop-down menu, select Mobile services.
3. Under “Manage your phone number,” select Manage.
4. Select Find a new number.
5. Choose the province and city for your new number.
6. Choose a new area code and the first three digits from the drop-down list, and select Next.
7. Choose a new phone number.
8. If no phone numbers appear, select a new area code number and search.
9. Select Next.
10. Review your changes and select Submit.
11. You’re done! Your new phone number will be confirmed.