I have a question -

The Problem -
I was taking backlit photos of my Grand daughter, and my ancient 85 1.8 Nikkor was having trouble focusing.
I was in a darkened part of the rumpus room and my GD was in the centre of the room with a far light behind her head
Settings where ISO 100 @ F2 - spot metering. Nikon D7000.
I would press the shutter and it would not fire on every second shot.

The Question -
Would increasing the ISO have any effect on the lowlight focusing.
(Had I thought of it at the time I would have tried it out.)

Any thoughts?