I read the novel, and have some personal familiarity with the Lyon case. I think the author would have been wise to set it in a different year, a different season, and perhaps outside of Maryland. But I don't think it resembles the facts of the Lyon case much at all. No one in the novel remotely reminded me of any counterpart in the case. It is not great fiction, but few paperback mysteries. I don't think the author was exploiting the situation; if so, she would have written it 30 years earlier. I don't think the Lyons were the least bit affected by it. They have dealt with far greater indignities and insensitivity.
I have to agree with Thrasher on this. I've read the book and, while I wish Lippman could have changed a few more minor details to deflect comparisons, the plot of the book bears almost no resemblence to the Lyon family's story. It uses the basic idea of two girls disappearing from a mall as a jumping off point, but the story is mostly focused on the present and the psychological/emotional effect the children's disappearance had on those involved. It's only nominally even a mystery.
I doubt the book has had much effect on the Lyon family, except perhaps to generate some renewed interest in the girls' disappearance, which is a good thing. I always hope that one of these days someone will come forward with a new piece of information that makes the difference. That has a better chance of happening if the public is occasionally reminded that the case is still unsolved.