The IP address of her local machine will only allow you to connect to her server if you are on the same local network, in other words plugged into her router or using her wifi. If you want to connect from outside her local network she'll need the internet IP address from her router, and she needs to enable port forwarding to tell her router where to send queries to the Electrs port (usually 50001.) Take note, if her internet service provider uses CGNAT, you won't be able to connect to her server from outside her local network unless she has a virtual private network set up, or uses TOR. TOR is by far the easiest way to get around CGNAT for personal use.
To find the server's local network IP address use the following commands:
Linux:
ip add
Windows:
ip config
To find the internet IP address the easiest way is to log into the router's configuration page, you'll find it listed there. Once in the router's configuration page you should be able to set up port forwarding there.
No, she doesn't. Not unless she has a VPN running on a cloud server or some complex set up of that sort, but given the questions being asked here I gather that's not the case. The only reason she would even need such a set up is if she didn't want to use TOR and has a service provider that issues IPs through Carrier Grade Network Access Translation (CGNAT,) such as satellite internet, cable internet, or 5G internet services.
If her ISP uses telephone-based land-line connections like ADSL or Fiber, her router will be issued an IP address that's reachable from outside the local network.