You make it easy for them to get up if they make up their mind to get up, because once they make up their mind to get up they are going to. Even if they have to climb the guard rail mountain.
I think what you are dealing with here is a recommendation for the general population that doesn't fit for the patient with dementia. A rational thinking adult, even if elderly and sick, would know to stop at the guard rails. The patient with dementia just sees it as something to go over..... much as a toddler does. We know when to take the toddler out of the crip... when they climb over the rails
So make the bed a height that is easy for her to stand up. Remove any sharp corners that might injure her. The less around her bed the better. Get the monitors and use them. If she continues to get up and down during the night you might want to hire a sitter at night to watch her so your Dad can sleep. Nothing like another pair of eyes to help.
Beyond that, know that our loved ones with dementia are in their own world. They rarely do what is expected and sometimes they hurt themselves. We can do all that we know to do and all that we can... and they will find a way around our safe guards. Short of the bubble world you mentioned there are no 100% guarantees.