In just about every version of Windows, the amount of time it takes to get to the desktop continues to decrease. This is due in part to better hardware but also Windows has become more intelligent with what it loads and precisely when it does it. This has resulted in the desktop loading faster after login, but your PC may be extremely slow right after the desktop displays as the start of many apps and utilities were simply deferred.
We need to address the root cause of the slowdown, which is really the loading of multiple applications triggered by the startup. In the latest version of Windows 10, this is incredibly easy to do. You could even guide your Mom through it over the phone.
Just click on the Start Button, type in Startup Tasks and hit Enter. The Startup Apps section of the Settings App will load. Next, just hit the off switch next to any apps you don't really need starting up automatically.