The answer mwestwood provides gives you all the information you need, but I would caution you that we learn nothing about anyone in this story ... we have a lot of very strange things happening, things outside the "laws" of physics ... but it's all ambiguous. It happens in the forest, the home of the devil, a place where anything can happen. The evidence would be hard to believe IF Brown were certain that it happened, but we don't even have that much evidence ... Brown thinks it may be a dream, the dew on the leaf suggests that this is the case, but we don't know (and for Brown it doesn't make any difference since the experience wrecks his life).
But to use this "evidence" to suggest that there is evil is Goody Cloyse is a bit of a stretch. It reminds me of the spectral evidence in "The Crucible" and we know where that went ....
A real person who was involved in the Salem Witch Trials of 1692, Goody Cloyse is recognized by Goodman Brown as he walks with the old man with the snakelike staff. Ironically, when Goodman espies her, he tells his companion,
"But with your leave, friend, I shall take a cut through the woods until we have left this Christian woman behind. Being a stranger to you, she might ask whom I was consorting with and whither I was going."
And, his fellow traveller agrees, "Betake you to the woods, and let me keep the path." Then, Goodman goes, but he watches the old man who comes close to Goody and touches her neck with "what seemed the serpent's tail."
"The devil!" screamed the pious old lady.
"Then Goody Cloyse knows her old friend?" observed the traveller, confronting her and leaning on his writhing stick.
"Ah, forsooth, and is it your worship, indeed?" cried the good dame. "Yes, truly, is it, and in the very image of my old gossip, Goodman Brown. The grandfather of the silly fellow that now is. But,--would your worship believe it?--my broomstick hath strangely disappeared, stolen, as I suspect, that that unhanged witch, Goody Cory, and that, too, when I was all anointed with the juice of smallage, and cinquefoil, and worlf's bane"---
"Mingled with fine wheat and the fat of a new-born babe," said the shape of old Goodman Brown.
"Oh, your worship knows the recipe," cried the old lady, cackling aloud...."There is a nice young man to be taken into communion tonight. But now your good worship will lend me your arm, and we shall be there in a twinkling."
But, the "good worship" only gives her his staff that he throws down; it forms the shape to which "its owner had formerly lent to the Egyptian magi. Goody disappears and Goodman reappears to say with dramatic irony, "That old woman taught me my catechism." Hawthorne then writes ironically as narrator, "and there was a world of meaning in this simple comment."
With her immediate recognition of the old traveller, the devil, Goody Cloyse establishes herself as evil. Then, when she speaks of her broom and the old man offers her his staff which transforms, indications are clear that Goody Cloyse is evil herself.