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That sounds like a nice gift for your sister! What type of services did she want -- pre-paid or post-paid? Was the new line going to be on your account or her own account?
If her line was going to be on your account, you could choose the Add a Line option via your My Account. You could then select the plan for her. You should note that adding a new line might require an additional credit check if opting for post-paid services. Once the line is set-up, you will be sent the new SIM card.
On the other hand, if the line is to be set-up on her own account, I think she will need to sign-up for services for herself. She can do so via Fido.ca. If she wants a post-paid option, they would likely require a credit check. A credit query would not be required for pre-paid services.
Hope this helps 😀