The test with 127.0.0.1 can only work if you have a samba server setup running on your Netrunner already.
You can easily do this by right clicking a folder and sharing this folder.
Then your network should appear also in the filemanager network -> smb or smb:// folder.
As for the secondary pc you want to access try pinging the IP Address to make absolutely sure you can reach that PC. So open a console and type in:
ping 10.0.0.252 and see if you get an answer from your other PC.
If it does not answer then you have an issue with your network somewhere. Check if the Primary and Secondary are on the same net and subnet addresses or same address space.
Then ultimatively you can try mounting also via the terminal what could give you a better error message when it fails.
So first create a folder to mount your Secondary PC.
Type in the terminal:
Then we mount the Folder (in this example Public, change it to whatever folder you want to mount from your wifes PC)
Username is the username of the share on your wifes PC. Adapt it aswell
sudo mount -t cifs -o username=leszek //10.0.0.252/Public ~/secondary-share
It should ask you for the password to access this computer and after entering it it should return without an error message to the normal terminal prompt.
Then you can open dolphin filemanager and go into your home folder and the subfolder secondary-share and see the shared foles and folders of the secondary PC.
Otherwise it might show an error message which can help us further to figure out what is going on.
Hope that helps. And thx for your patience.