If Windows 10 is in S Mode, she can only install Apps from the Microsoft Store, she cannot install 3rd party applications
You can switch Windows 10 out of S Mode to Windows 10 Home, it costs nothing to switch and then she can install that software . . .
Open the Settings App
Go to Update and Security - Activation
In the Switch to Windows 10 Home or Switch to Windows 10 Pro section, select Go to the Store. (If you also see an "Upgrade your edition of Windows" section, be careful not to click the "Go to the Store" link that appears there.)
On the Switch out of S mode (or similar) page that appears in the Microsoft Store, select the Get button.
After you see a confirmation message on the page, you'll be able to install apps from outside of the Microsoft Store.