You need to get the rose .stl from here; https://www.prusaprinters.org/prints/131488-spiral-vase-rose/files
Use the “VaseRose_7cm_withbottom.stl”, “VaseRose_5cm_withbottom.stl” or “VaseRose_FullSize_withbottom.stl”.
To attach the rose to the stem, you need to glue it on. I use the Locktite Brush-On for all of my prints where glue is necessary, but any glue for plastic works. https://www.loctiteproducts.com/en/products/fix/super-glue/loctite_super_gluebrushon.html
Update 14/2: more thicknesses and an ”organic“ version added.
The stems can be found with the following thicknesses:
5cm version
7cm version
Full version
The pictures added by me are the ”organic“ version with the 7cm rose (white) and with the 5cm version (blue), 3mm version with the 7cm rose (red) and 5cm rose (yellow). The 3mm version is very much on the limits of the rigidity while printing, so a well tuned printer is required. The 4mm and 5mm versions are much more rigid and forgiving. The organic version looks better but is more complex to print.
The author remixed this model.