Don't know what the 2019 yaris is like but my 2006 yaris with 335.000 KMs on the odometer regularly sits in the drive for a week, sometimes two at a time without moving. I had a battery die on me after towing a caravan in 38°C weather with it for a whole day. This was in 2018, that battery lasted me until last year when the mechanic told me it was going down and needed replacing. All this to say that unless Toyota has gone to absolute shit over the years then I'm guessing something isn't quite right with your mum's yaris.

(okay yes, I also wanted to put my trooper of a yaris in the spotlight. My first car ever and the best deal I will ever make in my life).