Why didn't Mary...(spoilers)

Why didn't Mary leave with them at the end? She had no kids, she hated her mother, she had no more pets(since Dick killed the ones she loved), her friends were barely past acquaintances, and she was an anthropologist. She basically lived to discover other races and foreign cultures.

If there was any indication that she should have left, all signs pointed away from Rutherford.

I think they missed a huge step at the end there, and if anything, she would have gone with. She barely had a reason to stay, especially to see what else existed in the great beyond.

Also, unrelated, the IMDB phone app is atrocious. I sign in to the forums, and it brings me back to the main page--signed out. I sign in at the main page, and then try to post at the forums, and it still says I need to sign in, despite having a sign out option at the top right. /mini-rant off.