I guess you haven't gotten xylazine over there yet
I've been out of that game a long while but as far as I know, no. The UK junkies seem to be better at rejecting shite and if no one buys it, dealers don't try. Even with fent, cos it is really shit in comparison to heroin- if you're lucky it just sends you unconscious for a bit then you come round rattling, if you're not, well.... But no one liked it, and news of whose got good and shit drugs moves fast in those communities, so they can't sell it.
I really don't understand why the American market didn't do the same.
Also it doesn't sound like she' really doing much street heroin, she claims to have been on methadone for 16 years but still has teeth which is somewhat fishy. If she's got any nous she'd figured out how to use a dark web market.
Thinking more about what they might be putting her on and drawing a blank. Drugs similar are actual diamorphine, morphine. Oxy would be a definite no. There's a bunch of weird synthetic opiates so maybe one of them. I think they want her in withdrawals so they can get a full handle on her habit, how quickly and how intensely they come on will tell you if she's been dbbling on top of her script, or not taking all of it or whatever. You can't just take addicts at their word.
Still can't get over her bitching about not getting drugs when and in the amounts she desires in fucking rehab (which is probably actually detox).