She is not correct.
You cannot just interchange given variables unless you are solving for an inverse relationship. If you are just solving for one of the variables where you have to adjust a formula, you do the inverse operation; you are not finding the inverse formula.
A is wrong
She is interchanging parts of a formula. You can't do that when you are solving for a different part of the formula.
C is wrong
She is inventing a new meaning for the word commutative. Commutative just means interchanging to order variables are written. ab is commutative with ba. You can never cross over an equal sign to show commutative properties.
D is wrong
She is intermixing adding and subtracting with multiplication and division.
B <<<< Answer