Meh, it's too J-Lo for me. Yes, I have seen J-Lo and Liz Hurley wear stuff like that. I never liked their style and I feel it's all wrong for Helena's personality. She's a school-teacher, someone who likes to put the fear of God in men and who KNOWS understated elegance works best to look sexy without having a slew of men trying to get handsy with her.
See, that dress shows off too much to be tasteful, IMO. If you show off the back, you must either be better covered up in front or if not, your legs should be covered. If you're going for a super-short skirt, show less cleavage. If you're going for plunging neckline, cover your back and wear a long skirt with a single thigh-high slit. And esp if you're going for a daring plunge-to-belly-button like that, keep the rest of you fully covered.
The line between sexy and slutty is in knowing exactly how much to reveal.