She could stop time for a couple of seconds and stab Akainu through the heart in that short window, but I doubt she’d use that ability immediately at the start of this battle.
She’d probably begin by hurling icicles and then ramp up to larger ice spheres to throw, but I doubt that would be very effective against Akainu, who’s strong enough to smash through those ice blocks, if his magma isn't straight up hot enough melt through most of them.