She's probably thinking something similar to a game like RIFT.
Where abilities that pierce elemental resistance, take 10% away from the actual points rather than the resistance directly.
So if 200 s 20% elemental resistance.
10% elemental piercing would b

200 - 20 = 180 = 18% elemental resistance for the ability.
Which would be a 2% or so increase.
FFXIV and FFXI dont do that thankfully