Double specific chainset moves the chainline out so there will be more crossover when in the outer and 36 than there is on a triple converted to double.
A cheaper option would be to get her to change down to the granny, I generally avoid using the last 2-3 gears when in the outer ring (converted triple) so as to avoid excessive crossover, but yeah a triple would help by moving the chainline inward
Did you end up fitting the double specific 11 speed Shimano mech?