UF6 sold to Russia and eventually to North Korea.
Iran takes hostages. "Negotiates" for their release. Obama sends them billions in cash shrink wrapped on pallets. 2 planes in the air full of cash. Only one lands in Iran. The other NK? Cash is untraceable. Works to facilitate the U1 transfer.
All evidence that I know of at this point is circumstantial. It could be related to why Trump kept pushing her to release her medical records. Her symptoms such as uncontrollable muscle spasms and emotional outbursts seem to fit.
You could do an isotopic analysis to determine where the uranium came from if it were in metallic form or in a natural state. However UF6 is highly purified. Think distilled water… It would be very difficult to trace impurities, but if they are there in sufficient quantities, you may still be able to determine the mine the uranium came from.