Why does Hester meet Dimmesdale in the forest to warn him about Chillingworth?

She needs to meet him in order to warn him about who Chillingworth really is. She wants to let him know that Chillingworth might actually want some sort of revenge.

Again, the forest has become a place of truth and reconciliation as opposed to the village which represents the opposite.

They also decide to leave for Europe, with their daughter pearl to start a new life without shame.

to warn him who Chillingworth