This has been my experience after I installed Fedora on my folks' laptops. Pretty much the only support they've required is the occasional major version upgrade I do for them when I visit. Regular patches get autoinstalled.

They'll use Wi-Fi or USB tethering with their phones for internet browsing and my dad will occasionally connect the laptop to the TV set to watch some videos, and it all just works.

Because it's far more likely she'll run into some kind of problem with hardware or software incompatibility. And why does her computer make such a noise when she's watching Youtube and Netflix? And why did her touchpad suddenly stop behaving like it used to after a system upgrade?

There are problems with Windows and Mac for casual users too, but it'd be sugarcoating things to say that Linux isn't far more likely to spuriously act up.