her peeing in the others wheel is a way of saying this is mine not yours. This is a dominant act. I just want to say do you check your hams over every day? although you watch them you may not see an injury if one flees from the other after being bitten. Even if they still spend time together and sleep together this does not mean that they could still not be hurting each other, because they could.
just keep and eye on it and be prepared with another cage if you have to separate them quickly.