So why did she say she's pro-choice? Because she knows better than to "come out" as pro-life.
You're wrong IMO. She said she's pro-choice because, aside from the issue of whether a child has DS, she believes women should have the choice to terminate or not. So basically 99% of the time, she's pro-choice.
Even in the DS scenario, she technically believes they should have the choice but she doesn't like the social and medical context in which these choices are currently being made.
So does maybe restricting women's choices 1% of the time make you 100% anti-choice? No more than a horse with a skin graft grown on a pig would be a pig...you're right, it was a stupid comparison :)