  Graphene, with its massless linearly-dispersing carriers, in the quantum Hall
regime provides an instructive comparison with conventional two-dimensional
(2D) systems in which carriers have a nonzero band mass and quadratic
dispersion. We investigate the influence of Landau level mixing in graphene on
Wigner crystal states in the $n^\mathrm{th}$ Landau level obtained using single
Landau level approximation. We show that the Landau level mixing does not
qualitatively change the phase diagram as a function of partial filling factor
$\nu$ in the $n^\mathrm{th}$ level. We find that the inter-Landau level mixing,
quantified by relative occupations of the two Landau levels,
$\rho_{n+1}/\rho_{n}$, oscillates around 2% and, in general, remains small ($<
4%$) irrespective of the Landau level index $n$. Our results show that the
single Landau level approximation is applicable in high Landau levels, even
though the energy gap between the adjacent Landau levels vanishes.
