There are a few ways you could remotely administer it:
1 - Port forwarding. You'd port forward the http, server and rtsp ports to the IP address of the NVR. The NVR needs a static IP address for that and you may need Dynamic DNS depending on the provider. If it's Virgin Media it's easy as their IP addresses virtually never change but BT, Sky and all of the others do. If you needed to access a camera menu directly you'd also need to forward ports 65001 to 65004 (for cameras 1-4 via virtual host)
2- VPN. You'd need the router to support a VPN server (most providers standard kit does not). Once your VPNs client (PC, Mac) establishes a connection, you could access the NVR using it's IP address as if you were there.
Options 1 and 2 are both problematic with regard to security, privacy and web browser support (often you can't see the video to alter event settings). My recommendation would be:
3 - Register a Hik Partner Pro account. You could then administer the system when needed from the app. Importantly, she would have control over whether you could view, play back footage. If there's an issue to look at you can request permission in the app to view/playback and she can accept in hers. If you view, playback, configure her app gives a service notification. If there's a fault you get a notification.