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One of the great limitations of an advice column is that you only get one perspective on the situation, and you are forced to take the words of the letter-writer at face-value. My preliminary advice would be for the person seeking advice would be to reflect a bit on their own motivations for singling out their attention on this person. This suspicion may be misplaced, but just for a moment I might point out that the part about confiding in the other teacher that you "feel very close to" might be read as you going to a friend to have your opinion validated or to recruit an ally, rather than seek an objective opinion. Also, as far as the unanswered questions in the question box, cant you or someone else assert themselves ten minutes before you finish class to address them? There are three other teachers.
Now, having taken care of some of the caveats, it _does_ sound to me like this woman has boundary issues. As far as whether the comments embarrassed the students, you really have to be there to get an accurate read on the situation. It depends on the exact contents of what was said, the nature of the specific kids in question, the woman in question, and their mutual relationship.
Also, it should be mentioned that sex is a very touchy subject (heh heh) and when it comes to talking about it with other people's 13-year old children, a little discretion goes a long way. Most health educators Ive been in the presence of may joke about things a little, or tell a story or two, but they also seem to take exceptional care to make sure they establish some line of intimacy that doesn't get crossed.
So, basically, talk to all of the other teachers about your concerns with the question box, and tread lightly but talk directly to the woman in question. If she responds reasonably, problem solved (for the most part). If she is inclined to act up following a confrontation [in a way that adversely affects the teaching of the class, or the working relationship of the teaching group], the other teachers will have little choice but to address her. The committee should be an absolute last resort-- it would be embarrassing for her, and it seems unlikely as well that the desire of the group for consensus wouldn't be able to successfully moderate a disagreement.