OK, so she can give ammo to other MGs in same echelon and decreases enemy stats while she's reloading. The actual interesting part is that any ally on her buff tiles gets a special buff that makes enemy hits deal 5 damage. Not "capped at 5 damage", every hit does 5 damage, period, whether it does 1 damage or 1000 damage. They take 5.

M26 MASS ignores damage of 5 or less (or 8 or less with flash ammo), effectively making her skill a "Give MASS invulnerability" skill.