Hardy called it "seduction"

At the end of the fifth "phase:"

"The three o'clock sun shone full upon him, and the strange enervating conviction that her seducer confronted her..."

Nowhere else does Hardy mention the act (as narrator), so those who insist she was raped are just poor readers. Plus when she confessed this experience to Angel you would think she would have mentioned being forced physically if that were indeed the case, which it was not, making her confession all the more poignant.