You cannot add her to your Norton Account. But if you have a current subscription with available activations she can install Norton on her device using one of your activations.
I see you noted iOS in your post. If your spouse also has a mobile device, you will have to either sign into your Norton Account on her device to activate 360, or give her your credentials for your Norton Account so she can do it herself.
For a Windows system, you send her a download email from your Norton Account. When she opens that email just follow the instructions to download and install a pre activated copy of 360.