Yes, ISR/Oldenburg will inspect her and, assuming she gets passable scores, will be entered into the Pre-Mare Book. Her foals by approved stallions will be registered and branded ISR (International Sporthorse Registry).
I have a branded, but no papers Dutch. Pretty sure know sire, but dam line unknown. thinking about breeding her. What registry MIGHT register foal, thinking OLDna/ISR or RPSI.
If you know her age in addition to her sire, I would think KWPN should be willing to help you figure out her lineage. I know some of the German registries are able to search their database by foaling year for foals by XXX stallion, and then use color/markings to ID a horse. Now whether they will issue duplicate papers is a variable - some will, some won't without a bill of sale from last owner of record.
But why don't you have papers? Were they not transferred from previous owner? Does the previous owner claim she never had the papers and they were "lost" beforehand?