since i don't know the student's actual proficiencies, nor where her particular weaknesses lie, my recommendation would be to go to https://www.khanacademy.org/exercisedashboard and take some of the exercises there. start at the top and have her work her way down.
my guess, based on the scant information you have provided is:
a lack of knowing how to manipulate fractions.
a poor understanding of the distributive law.
lack of seeing that percentages ARE ratios, and what they MEAN.
unfortunately, with our given system of arithmetic (arabic numerals in a base 10 system of digits), a certain amount of memorization is mandatory. you simply cannot multiply 24 x 37 if you do not know what 4 x 7 is.
some understanding of the "laws of arithmetic" is in order, too. does she know what "additive identity" and "multiplicative identity", or "associativity" and "commutativity" mean, and how to use them to solve problems symbolically (like with x's and stuff)? these rules aren't just "more meaningless stuff to learn" but are "labor-saving tools" if you know 4 x 7, you don't NEED to remember what 7 x 4 is, if you remember the "commutative law".
frankly, i am surprised she does as well in her classes as she has been. one suspects the school system has been kinder to her than warranted, and it does not sound like she is anywhere near prepared for "hard courses" like analytic geometry or calculus (which is FAR tougher than calculating a 15% discount on a pair of $20 shoes).