I think where you're naive OP is believing 'everyone' in her circle is doing it.
I used to go to parties with lots of people v into the club scene - DJs, etc. Quite a few of them were VERY into their party drugs. I would say there was a core group of them who were all extremely regular recreational users, and yes lots of them were professionals, etc etc.
Of a larger group, where it was 'normal', it was still only maybe an average of 3 out of 10 people who were doing it. Everyone else might have a joint if it was passed around, but weren't interested in the pills. There was a small group who were v regular users. Of that group, of maybe ten people, I know two whose lives ultimately broke down because of the coke - the others matured, settled down, only used it recreationally, but these two couldn't stop, lost jobs and marriages.
I have one friend who was an exceptionally heavy coke user in his twenties and quit and is pretty open about the fact he thinks he has some form of brain damage, which I'd agree with - basically there's something v particular about the way he processes info, quick to anger, he has a number of traits I'd associate with other heavy coke users but he has definitely been clean for over a decade. However, he was literally working in the music industry and doing it daily.
On balance though, I think regular (weekly) use is not actually as 'normal' as she makes out. There will be people who go out and do coke/MDMA every week. There will be more who do it at festivals/birthdays/'special occasions'. There will be more who don't.
And in that group of v regular users, most will be fine with it, will be able to cut back and take it or leave it. But, quite a few will struggle with, not necessarily addiction, but feeling reliant on it to get a buzz. Some of those will potentially get into financial details. A smaller number will really, really struggle to quit.
I used to be fairly laid back about drug use: it was never my scene, aside from the odd joint, but I mostly had ethical reasons around production lines. I didn't think everyone was going to become an addict. Now this cohort of people are all later thirties/early forties, and I've seen the outcome, I think a bit differently. I know two regular week smokers (since their early teens) who have been diagnosed with drug-induced schizophrenia, and a handful of people with lost marriages/jobs/long-lasting effects from their coke use. I feel a lot more cautious about it now.
Nobody knows who has addictive or depressive tendencies that could be worsened by these drugs till its too late. I wouldn't be as cavalier as you're being - I think at a minimum, I would be recommending her to make sure she takes regular weekends off, cautioning her about some of the risks. Because you're her mum, and that's your job.