It seems that it is not possible to see the GPU memory usage with nvidia-smi while you have a display connected to the GPU in Windows, according to this Stack Overflow answer: https://stackoverflow.com/a/44228331 10
Another option seems to be an API (https://developer.nvidia.com/nvapi 12) that lets you see GPU info on Windows, but I have not tried since I work on Ubuntu.
As a last resort, you could come to Linux, we have penguins and cookies!