She ist left-handed, and we couldn't find some any option to remap the mouse buttons.
For some courious reason the mousebuttons are left-handed in the main-menu, but in the game they are right-handed.
It works for me on Linux/KDE - when I swap the mouse buttons in the system settings, they're also swapped in Crayon Physics Deluxe (both in the menu and in the actual game).
Which operating system are you using?
Which version of the game are you using?