The first movie sounds exactly like the awesome Bette Davis film The Nanny.
This is the synopsis of the movie (taken from IMDB):
Bette Davis is an English nanny whose charge is 10-year-old Joey, just
released from a home for disturbed children where he'd spent two years
undergoing treatment for drowning his little sister in the bath.
Shortly after his arrival home, suspicion arouses again when his
mother is poisoned. But Joey continues to insist Nanny is responsible,
just as she was with the death of his little sister, with only a
neighboring friend believing the young boy.
Okay, so the second movie sounds very like Eye for an Eye. It's about a woman who overhears her daughter's brutal rape and murder on the phone, and has some scenes similar to what you describe. From RogerEbert.com:
The movie stars Sally Field as Karen, a mother whose teenage daughter
is raped and killed, in a particularly horrifying scene, early in the
movie. The daughter calls for help, and Karen actually hears the
attack over the telephone - and then tries to race home, gets stuck in
traffic and is trapped in a nightmare scene where other drivers refuse
her request to use a mobile phone.`
The Wikipedia page for the film describes the ending:
Karen sets a trap to lure Doob into her home, so that she can say
killing him was self-defense. It works. After she shoots Doob dead and
calls the police. Denillo arrives and tells Karen that he knows the
truth and that she hasn't fooled him, to which she replies "prove it".
He decides to tell his colleague that it was a "clear case of
self-defense". When her husband arrives, he sits beside her, holding
her hand, knowing what she has done.
Based on your descriptions, these two films sound most likely. So in summary:
- Nanny Tries to Drown Girl: The Nanny
- Killer calls mom, kills daughter, then tries to kill mom: Eye for an Eye