To make my explaination more helpful, i will describe you the step to buy a sim and add a line with ease!
To add a line from Fido.ca, you need to login in your My Account Dashboard at Fido.ca, then after you click the add a line link from your account dashboard. After this there will be prompt a prompt for selecting your plans data/options, Caller Name ID and you will be asked to choose a new phone number. It's easy like this !
Have a nice day
Welcome to the community!
If you do not already have a line for your daughter, you would need to add a line for her. You should be able to Add a Line via your My Account. As already mentioned, it is also possible to add a line via customer service or Live Chat. However, you should note that having a service representative assist with the addition of the line would likely incur an activation fee. However, I believe you can save the Set-up Service Fee when you activate online yourself.
Hope this helps 😀