Best plan would be to use normal oranges not Seville, blood oranges for examples make a sweet marmalade.
My goals are the opposite since I love bitter, I stopped using a recipe that called for leaving out half the pith as it was not bitter enough. So she could try that (pair the zest first, slice orange in half and juice then don't use the pith at all) and use powder pectin from the store or apple or lemon
