The star, whose character Anna Bates was attacked by Lord Gillingham's valet Mr Green in Sunday's edition, said it was a brave move.
ITV warned viewers about upsetting scenes before the start of the drama, created by Julian Fellowes, but had still received about 60 complaints by yesterday, with Ofcom also receiving an undisclosed number.
Froggatt said: "I was really proud of the show for tackling a subject like this. It's a really brave thing to do and I believe Julian's written it in a way that is not gratuitous at all."
Froggatt said the creators did not want to show graphic violence on screen. She said: "The shock value was there without having to depict anything graphic."
She said she had prepared for the role by looking at the testimonies of women who had been through a similar ordeal.
She added that the show's historical advisor had pointed out that women still had few rights back then which made them reluctant to report such an attack.
She said: "There was still such a stigma attached to any sort of attack like this."
The episode was seen by an average audience of 9.2 million according to overnight figures.