Interesting. My sister is left handed too. Her computer is in the living room 'cause it's technically the "Family" computer, but everyone else has a phone, laptop, tablet, and/or desktop. So with hers being a desktop I could go upstairs and watch her use the computer. I've never really done that, so I just assumed it was the same as everyone else.
Or like my other Sister with fencing. Basically, left handed fencers have an advantage due to most people being used to fighting a right handed person, so my sister learned how to fence left handed (Though she's ambidextrous, with a right preference) so she can have that advantage. Maybe Ivy just learned to use her right hand before she went straight to left.
Idk, I'll talk to her tomorrow about it lol