I saw this movie while on vacation.
The mother is killed by the nanny. The mother's sister figures it out: the nanny was the dad's lover (hired as a nanny to continue the affair). The dad, who is a doctor met her while traveling for a conference and brought her home as a nanny.
I don't remember much else. I saw it on HBO. I thought the title had the world 'affair' in it or 'secret' or something but I went on IMDB and checked out most of those titles and no luck. I saw it in June 2011 or June 2010. Not sure which one.
Please help identify this, I never got to finish it and its been haunting me for years