Can the Harm spell kill with massive damage?

Question

Scenario

We fought a daemon that used it's Harm spell-like ability on a player, dealing 100 points of damage on the player's failed save. The DM said to make a massive damage¹ roll. The character failed the massive damage save and died.

It was then argued, since Harm can't bring a hit point total to less than 1 hit point², she shouldn't have to have made a massive damage roll in the first place.

Our GM then stated, she died due to massive damage, not the spell itself, therefore is a different source, and is still dead.

My character raised her soon afterward anyway....

---

Question

Can Harm, not being able to reduce a hit point total below 1, kill through massive damage rules?

---

Footnotes

¹_{Massive Damage (Optional Rule): If you ever sustain a single attack that deals an amount of damage equal to half your total hit points (minimum 50 points of damage) or more and it doesn't kill you outright, you must make a DC 15 Fortitude save. If this saving throw fails, you die regardless of your current hit points. If you take half your total hit points or more in damage from multiple attacks, no one of which dealt more than half your total hit points (minimum 50), the massive damage rule does not apply.}

²_{Harm cannot reduce the target's hit points to less than 1.}

Answer 1

Your DM is correct.

Note the following wording in the massive damage optional rule (emphasis mine):

If you ever sustain a single attack that deals an amount of damage equal to half your total hit points ... or more and it doesn't kill you outright, you must make a DC 15 Fortitude save. If this saving throw fails, you die regardless of your current hit points.

First, the massive damage rule is only triggered if you survive the damage, so the fact that Harm can't reduce you below 1 hit point makes it more likely to trigger massive damage.

Second, failing the massive damage save kills you no matter how much HP you have. It explicitly says so. The fact that Harm leaves you with at least 1 HP make no difference because it's not the HP loss that's killing you.