Like Boiler said above it largely depends on the country she’s in. It’s typically not good testing positive for cannabinoids. Worst case she could be inadmissible, best case they look at her medical information and approve her. Because cannabis is federally illegal, it is still generally frowned upon even for medical consumption.
In our experience (country Morocco, k1 visa), just admitting to previous use a couple of years prior (no dirty test) landed us about an 8th month or so delay in getting approval. Initially we were told it would be a year long process with 4 drug tests. Ultimately he didn’t have to complete all 4 test and was approved.
Morocco is a difficult country for visas due to fraud. We also were not married. So hopefully things go well for you both. Best of luck.