She has had a finger jabbed into her arm by a member of the Rev Ian Paisley's Democratic Unionists, and been pushed against a wall in a corridor by a senior member of the Ulster Unionists. In the forum, which was set up as a vehicle for the talks, Mr Paisley has described her arguments as "red herrings - stinking, rotten red herrings."
Her speeches are interrupted by shouts of "silly women" and "stop wasting time". One Ulster Unionist member publicly told her to sit down and shut up. It has been a rough and unchivalrous baptism for a cross-community group of women who came into electoral politics on a tide of idealism.
"We've had to find a lot of courage to deal with it," says Mrs McWilliams. "When you're facing angry faces shouting insults at you, it takes an inner courage to maintain a calm and make your points over that level of acrimony
"We're representative of both communities - that confuses them, they don't like it, and it makes us the brunt of hatred, the brunt of venom. It has been quite devastating in the forum to witness raw, naked sectarianism."
Mrs McWilliams exempts from such criticisms nationalists and republicans - who in any event stay away from the forum - and the smaller parties who are associated with loyalist paramilitarism. She says it is members of the DUP, the smaller United Kingdom Unionists, and to a lesser extent the Ulster Unionists, who behave badly towards the women.
She says: "Ian Paisley Junior says that if we can't stick the heat we should get out of the kitchen. We can stick the heat - we actually want to be in it, the heat is what this is all about in terms of negotiations. But this is something else: we've been called traitors because we've said we're for inclusiveness.
"It's not just that it's an adversarial style: this is very sectarian, sometimes it's sexist, and it's personal insults as well. We've been humiliated publicly. A lot of these guys who are calling us traitors, and making us out to be something we're not, have minders, security people, police escorts. A lot of our women live in quite dangerous communities, and some of them have had difficulties because of this stuff. It can be dangerous."
Things are rather better, she says, in the private talks sessions when the media are not present. But she believes things will continue to move very slowly: "We're two months down the road, and we haven't even agreed the damn opening agenda - that's a problem."
But behind the scenes, she has seen attempts to build trust, and she reports that there is some goodwill and much respect for the former United States Senator, George Mitchell, who chairs the talks.
The summer marching season was, however, a bad setback. "It really created a terrible situation," she says. "It really shows us that the society is fairly dysfunctional at the moment, that we're not living in a normal society. I felt completely devastated - you have high expectations and then you get an awful fall. I had thought that the potential for creating some kind of accommodation was there, but clearly that was not the case."
Like many of the other participants, she will go to the talks today with more hope than confidence of success. "Although I'm very pessimistic at the moment, I feel I have to retain the optimism that there is a possibility that we can work towards some sort of inclusion.
"I'm trying to be optimistic, because I think if you just lived with thorough pessimism there would be no glimmer, there would be no reason for continuing. I have children, I want to live in this country."