the Earth has roughly (and we're speaking very roughly here) 7.5 x 10^18 grains of sand
Oxygen itself makes up approximately 46.6 percent of the crust and 30 percent of the mass of the entire Earth.
Earth Mass 5.97e24 kg
30% of that is about 2e24 kg or 2e27 g
O atoms are 16 g/mol
2e27 g / 16 g/mol = 1.2e26 mol
6.022e23 atoms/mole Avogadro constant
6.022e23 atoms/mole x 1.2e26 mole = 8e49
so 8e49 O atoms is much much more than 7e18, about 1e31 factor,
which is 10000000000000000000000000000000
now I did O atoms, not molecules, because she said "on the earth" which includes oxygen in rocks, which are not in oxygen molecules.
But even if you divide that number by 1000, it is still much much larger.
look at it another way, how much oxygen would it take for oxygen molecules to equal the number of grains of sand...
6.022e23 atoms/mole x M = 7.5e18
M = 0.0000125 moles
or multiplying by 32, that is
0.0003985 grams, a miniscule amount.