I don't want to insult Saberhead nor her friend, but I must ask whether or not they first removed the lock ring.

The cog goes righty-tighty lefty-loosey.

The lock ring goes the other way: lefty-tighty righty-loosey.

With a really tight cog, it sometimes helps to roll the wheel up against a wall and then use the chain whip in the direction of the wall while pushing down on the wheel so the wheel won't slip and turn.

Use a lock ring wrench/spanner for the lock ring and a chain whip for the cog.

My apologies if I've explained something Saberhead already knows.