We don't give a penalty if that action was directly caused by another illegal action. For example, a red blocker is back blocked by an white jammer, which causes red blocker to fall through the legs of white blocker, making white blocker fall. In that case, white jammer would receive a back block penalty, but there would be no low block penalty, because that contact was caused by the illegal action of the white jammer.
What you describe here does not sound like that at all. It sounds like the skater saw she was about to receive contact from an opponent (maybe she knew that contact would be illegal, maybe not), and decided to react by counter-blocking with her forearms. That counter-block was not caused by the illegal contact from an opponent, but an active decision. Based on that, both the direction of gameplay and the forearms should be judged individually based on impact.
In short: "reacting to" is not the same as "caused by"
