I was reading this question and was strongly reminded of a series I remember reading in my teens. This would have been a series of novels (possibly just one), published in English, and likely before 1980 - I read it in the 90s and it was fairly old, a used book. I do not think it is the same as the linked question, which is why I'm asking this separately. It was definitely a fantasy, not sci-fi.
At least two girls (and possibly also some boys/other girls) are transported from modern Earth into a fantasy world. I think they're a group of friends, possibly with some romantic pairings, and are in the 16-25 age range. The first significant scene I remember is two of the girls ending up in a city, where they are taken in by an older female artist (might have been a different creative type, like a sculptor/actress). She's lesbian/bisexual. At some point she attempts to give one of the girls a love potion, but they reverse it on her, so instead the artist falls in love with the girl and accompanies her for the rest of the books.
Twist: It's later revealed that the artist's friends recognized the love potion and removed it. She pretended to be in love and went along because she thought it would be interesting.
At some point at least one of the girls ends up basically being a magical sex slave/prostitute. I remember her being tattooed or painted - I think in blue - and also possibly given some magical jewellery/piercings that ensure her obedience/love of her owner.
I do not remember much of the over-arching plot, just a few disjointed pieces:
The world has chaos/wild magic storms. The books might have called them something else. Anyone or anything caught by these storms is transformed into something else entirely, so different objects or species. These show up throughout as minor plot encounters. I think they can be defended against with a special material. Near the very end, a large storm engulfs a major city, giving it entirely new architecture and transforming the inhabitants into green, hermaphrodites with a centaurish body structure.
I am not 100% sure this was the same novel, but I recall a secondary character with a secret - at night he turns into a woman (not just his body, but an entirely different person). At some point it's revealed that the woman was his lover, and he saved her life by sharing his body with her - of course, now they can never meet/touch again.