  We study collective electronic excitations in graphene in the integer quantum
Hall regime, concentrating mainly on excitations with spin reversal such as
spin-flip and spin-wave excitations. We show that these excitations are
correctly accounted for in the time-dependent Hartree-Fock and strong magnetic
field approximations, in contrast to spin-conserving (magneto-exciton) modes
which involve a strong Landau-level mixing at non-zero wave vectors. The
collective excitations are discussed in view of prominent theorems, such as
Kohn's and Larmor's. Whereas the latter remains valid in graphene and yields
insight into the understanding of spin-dependent modes, Kohn's theorem does not
apply to relativistic electrons in graphene. We finally calculate the exchange
correction to the chemical potential in the weak magnetic field limit.
