The last scene

Well, maybe not literally heaven, but more likely what she dreamed while/before passing away, yes.
Everyone in that scene was dead, none of the survivors have been present. That alone is a very obvious sign that she also passed on.

KaiMaster, yes and no. Those things happen, but are not shown. The final scene is a hallucination that Rose has as she is dying. She is aware that she is about to see Jack again and her brain is creating an image of how she knows him. The appearance of the bright light in the ceiling is the instant that Rose dies because it represents heaven.

I figured she was just dreaming…

All answers are wrong, or at least uncorroborated.

The Rose/Jack part of the story is pure fabrication, and that means whoever wrote the screenplay gets to play God here.

If the writer says she was merely dreaming, she was dreaming.

If the writer says she died and her particular version of heaven was the grand staircase on the Titanic meeting Jack and the other passengers she knew and liked (but strangely not her husband), then she died and went to her heaven.

If the writer says Rose's brain was fabricating an illusion before death, than she was imagining it.

So the answer is there is no answer to your question.