In the movie Return to Sender, Miranda says to William:
I watched my mother die. And she did a lot of things...
Earlier in the movie, it was said that she only found her mother after she had epilepsy seizure and wasn't able to get to her emergency medications in time.
I might be wrong, but to me it sounds like Miranda could have reached the emergency medications and save her mother, but didn't do it on purpose, to satisfy some curiosity by watching her mother die. Is this correct? This would also explain her total lack of sadness/grieving over the death of her mother, which her father mentions at some point.