I would just echo the excellent advice over using ADHD friendly systems to help with being tidy.
But also point out the elephant in the room, spending half your salary on weed. I used it for a while and spent no more than £10 a week until I got ADHD meds. Your GF sounds like she’s spending 30 X that give or take. That’s addiction, 10% of us get addicted to it. It will effect cognition; problem solving (lose IQ points), short term memory, motivation. It may also cause anxiety and paranoia, especially at the levels you suggest, that’s heavy use way above therapeutic level. Also it’s more damaging to the lungs than tobacco (you in-hail more deeply). An addict will be all or nothing, forget about reducing it. I’d encourage her towards her Dr, they have medical cannabis, maybe that’s the lure. Best of luck.