Why does this mirror, made using a glossy material, not fully reflect all the incomming light? As shown in the picture, I have this scene where I want to film this girl from her reflection in the mirror, and from the front I have lighted her face up for the shot, but when I render it with camera pointing to her mirror reflection, her face just appeared pale and unlighted. No matter how much I jack up the light strength (even to a ridiculously high value), it just stay this way.

I tried messing with light paths, limited and full global doesn't make any difference. higher or lower sample rate doesn't make difference. Tried several glossy mode, no difference either.

Anyone know why glossy behave like this? And, if I wanted this shot done properly, what can I do?
Make sure Render Settings > Clamp Indirect is set to a suitably high number, or 0 to disable clamping all together.