How small would we have to be to enter the 5th dimension?

She was a blundering whispery child-like woman with wispy hair and lost worlds in her eyes

Miniscule. We cannot even imagine this with our 3 dimensional brains. We would not have mass. No width, breadth, height or length.

What if we have been entering the 5th dimension for decades and no one ever knew. Can I figure it out?

She stole the room upon entering, yet no one even noticed her. It was pure magic. Like all those things we cannot see but know are there. Like the air we breathe.