With opiates you can drop down as much as you want to safely, the withdrawals aren’t like benzos or alcohol as there’s no real life threatening or dangerous WD symptoms. However you definitely won’t want to, because withdrawals (obviously) suck and will cause a disruption to your daily life if you’re not an unemployed shut-in. Being dope sick isn’t fun in the slightest, dropping down to 90 immediately is great but IMO if she can go lower without causing herself too much misery I’d advise to ASAP. 90mg is still quite a bit to taper down from without assistance from other drugs, especially if supply/time is an issue.
It’s not comfortable but dropping from a large dose to a much smaller one is far easier than going from a medium dose to none. You can, and likely will, still be in withdrawal from going from ~200 to 60mg instantly but you’ll adjust to that faster than going from 50mg to nothing if you spend too much time trying to lower a higher dose slowly and run out. I’m assuming either money or a source is an issue since you said you don’t have the resources for a slow taper, sorry if I’m wrong but either way your original idea of dropping low and tapering from there is IMO the best route.
There’s quite a few threads on oxy or opiate tapers in general, maybe check some out and see if you can source some of the comfort meds people mention. Not all of them are illegal/prescription either, but personally I’d advise against using stuff like Kratom or loperamide. While they won’t get you high like a true opiate(debatable for Kratom, I know, but it’s not a ‘true’ opiate high), they both can still cause dependence.
