How does Mrs. Putnam know what Ruth was doing in the woods?

Mrs. Putnam wanted Ruth to go to Tituba. She wanted to know about her children who'd died.

MRs. Putnam: Reverend Parris, I have laid seven babies un-baptized in the earth. Believe me, sir, you never saw more hearty babies born, And yet, each would wither in my arms the very night of their birth. I have spoke nothinN, but my heart has clamored intimations. And now, this year, my Ruth, my only - I see her turning strange. A secret child she has become this year, and shrivels like a sucking mouth were pullinN on her life too. And so I thought to send her to your Tituba -

Parris: To Tituba! What may Tituba - ?

Mrs. Putnam: Tituba knows how to speak to the dead, Mr. Parris.