Why the Uninvited title?
From what/how is the title derived?
Who/what was Uninvited?
Is it just a ripoff of the old ghost movie with Ray Milland from 1944? (Totally different plot.)
for them to have a reason to rip off the "old ghost movie" it would have to be relatively known or relevant, which it isn't.
the "uninvited" person that the title references would be Rachel who Anna hated having around her home, while the audience is probably misleaded into thinking it's about a ghost (for marketing purposes).