In addition to what /u/Sol33t303 said, if she has one of the larger ISPs you may be able to find troubleshooting tools by logging into her account. Many of these routers have built-in speed test and the ability to restart them remotely. Sometimes the ISP retains access to those tools for themselves, but sometimes they offer a way for customers to access them.

In the future you could install a Raspberry Pi with a VPN directly connected to her router via ethernet. It would give you a device on the network (behind her NAT) that you could reach if the router is online and allow you to troubleshoot issues with wifi or other devices. Just make sure it’s up to date and fairly secure, otherwise you might not be the only one with a backdoor.

You probably won’t be able to ping her router from outside of her network. If her ISP doesn’t offer those tools, the next best thing would probably be to contact the ISP support line on her behalf - maybe have her on a conference call so she can authenticate and grant permission to you. That way you can help translate what they are saying.