Mary's parents

Was it ever mentioned in the movie what happened to Mary's parents? Her grandmother seemed to be her primary caretaker and she was living in her house/mansion when not away at school but I just don't remember anything being said about her parents. I was thinking that maybe if Mary's parents were both dead, maybe died in a tragic accident, it could explain why she was such a troubled little girl and was lonely due to the fact that she had a hard time making friends in school due to her reputation of being a liar, schemer, and troublemaker. No I don't agree with what she did to Marty and Karen but this little girl was really was crying out for attention, love, caring, etc. Her grandmother spoiled her terribly and gave her everything she wanted (like most grandmas do of course who can afford to), but I think those things were missing from her life and that's why she acted out. I think she felt why should other people be happy when I was feeling so miserable. Marty was a handful and her grandmother couldn't handle her.

I can't help but wonder also what became of Mary after her grandmother passed on (assuming her parents were both dead).