In a big magazine, maybe. But for smaller magazines like Cune, that's not really standard.
Letting series continue is even more of a burden on smaller magazines.
Even MTK rarely will cancel a series with only one volume out.
When the first volume comes out they absolutely do look at sales to decide whether it will end at 2, maybe 3. They will even potentially cancel series at 1 volume based on reader feedback. What's rare is a manga ending suddenly without a final chapter that goes in the final volume.
That's not a good idea, because she risks losing trust and no one will buy her next works.
Whether it's a good decision or not really depends on stuff like the balance of their financial situation. It's not something an armchair expert like you can tell.
I'm not sure why you're bothered by it. Point is that an author cancel a series is never a good idea for them. Only situation I could see it being a good decision is if Cune doesn't allow hiatus, what yeah, we can't know if that's the case, although I never heard of a magazine doing that. But if it's just about the author current situation, a hiatus would make more sense. Konohana's author did that. Namori is doing it with YrYr. Even Prism, that we know will never be back is officially "on hiatus". It makes sense, as it's really hard to a mangaka to be published, to begin with.
So yeah, regardless of her current situation (what let's be honest, most people who bought her manga doesn't care at all), cancelling it suddenly without any explanation isn't good professionally speaking. I'm not even saying that she shouldn't. But that's how it is.