I have located a source for a refillable glass dome with a gasket, similar to the domes used in the snow-globes that gift shops often have at Christmas time.
This is speculation on my part, but I think it might work: crush the stem of the rose (so that the maximum amount of preservative may be absorbed by the flower's vascular system) and submerge the entire rose in a bath of glycerine, ethylene glycol, or even formaldehyde (stinky but a good preservative.) After it has soaked for several days, trim the rose to the desired size, and insert it into a glass globe like the ones at the site below. Instead of filling the globe with water, fill it with the preservative substance (glycerine, ethylene glycol, formaldehyde or such, whatever was used in the initial stage of preservation.) Once the rose is positioned and the globe completely filled, seal it onto a base with the gasket (also obtainable from the site below.)
As I said, all this is speculation; I have never tried to preserve a flower in liquid. The site which has the globes also has an email address which I presume belongs to a globe-creator: firstname.lastname@example.org. You might be able to obtain useful advice from this lady.
I have one other suggestion: instead of preserving the intact rose, has it occurred to you that you may wish to preserve only its sweet scent? It is not difficult to make scented oil from flower petals. I have often made my own perfumes in this way, and would be glad to help you do so. Some of our most persistent memories are linked to scents, not sights or sounds. By saving the scent of a rose, perhaps in a beautiful vial, you are catching and immortalizing the essence of the memory which this special rose represents.