I also thought that her 192.168.0.1 address was a little odd, but I've checked again.
According to her router interface, the internal network address is 192.168.0.1, which is her gateway address. Each additional device on her network is via DHCP and increments accordingly, e.g. 192.168.0.2, 192.168.0.3, etc. I tend not to use DHCP as I prefer static addresses all round.

GaryDrew wrote:
According to her router interface, the internal network address is 192.168.0.1, which is her gateway address. Each additional device on her network is via DHCP and increments accordingly, e.g. 192.168.0.2, 192.168.0.3, etc.

I'm not sure why they've used that terminology, but it seems clear that the Network Address in question is 192.168.0.0/24 - which is different to yours. Which is good

The phrase "Network Address" seems to be used in different ways, by different people. I don't know if there is an 'official' definition, as such, but this is the one I use :-
(from here: https://www.computernetworkingnotes.com/ccna-study-guide/network-address-basic-concepts-explained-with-examples.html )

IP address vs Network Address
As discussed, an IP address is the combination of two separate addresses, network address and host address. If we exclude host address from IP address, we will get network address. In simple term, a network address is an IP address without host address. In technical term, a network address is an IP address in which all host bits are turned off.

GaryDrew also wrote: I tend not to use DHCP as I prefer static addresses all round.

You could consider using the "Bind to MAC" function in the Vigor. This means every device can use DHCP, but gets the fixed IP address that you have assigned. It also means you can see the addresses you have used, without having to manually maintain a list elsewhere.
I use this method for my I.O.T. devices - where I need fixed IP addresses to enter into Firewall Rules. (I also keep the list in an Excel spreadsheet and get the two out-of-line, with monotonous regularity )

Sounds interesting, thanks for the tip. I shall investigate further.