So here it is: it turns out that Brooke was married to a mostly editor, slightly director named David Rawlins. His directing credit is an episode of Rod Serling's Night Gallery, entitled "The Tune in Dan's Cafe", which had as one of its co-stars, get this - Brooke Mills. Now, I'd found that credit before, but didn't know that the director was Brooke's husband. According to the book, one of Rawlins' most noted editing jobs was on Saturday Night Fever.
But wait, there's more. In the book, it turns out Brooke became pregnant by David around 1974, and they only had one child. This is where I think it gets interesting. Because Brooke stopped acting after 1977, when her child would've been 2 1/2 to 3 years old. Which makes me suspect that she retired from show business to raise the child, presumably drawing child support from the relatively successful David Rawlins. But that's just a theory.
So here's my inspiration. Even though I don't know where Brooke is, I might be able to locate David Rawlins. Big maybe, because there's one post on his entry from someone else looking for him, which isn't promising. However, if it's possible to find David, maybe he knows what happened to Brooke Mills. On the other hand, he may have died (IMDB isn't clear, neither are any references about him), so that would make it harder.
But I sure would still like to know what happened to her.