She isn't a literal Djinn, people just called people with powers that because they didn't have the language to call them mutants/meta-humans
Djinn is just how anyone with powers would've been called if they showed up 100 years ago in South Asia.
That's what the show went for
It's similar to the concept of the Eternals where ancient people couldn't grasp the specific concept of their being, so they were considered to be "gods", and the Deviants (particularly in the comics) was what inspired the stories of dragons, trolls, ogres, and other fantasy creatures.
One of the reasons I've always found mutants lame compared to the rest of Marvel is their lack of origin stories. The most popular X-Men have clear origin stories too (Xavier, Magneto, Wolverine).
I'd imagine it would be really tiring coming up with another origin story to why a normal person became a super-powered being. You'd get to the point similar to that Family Guy skit of Stephen King making a story about a lamp:
View: https://www.youtube.com/watch?v=tMZONL8x8NE
Just chalking the origin of powers down to "some energy mutating the body", "magic", or having alien DNA/are alien ("They are aliens so we know not of THEIR peoples' powers for we are just lowly humans, THEY come from another WORLD! COSMIC SHIT, BABY!!!").
It would eventually get to a point where someone gets bitten by a radioactive toilet and turns into a superhero called "The Flush".
Jesus I didn't realize this. All the bullshit "over my shoulder to reach my asshole" comments about how mutants have to be introduced via the multiverse and Marvel just straight up dropped mutants existing in the MCU already confirmation on us.
It's the slow build, like they seem to be doing for the Fantastic Four. First you had the nod to the existing Fox X-Men with Ralph Boehner/Fake Quicksilver (Evan Peters) in WandaVision, then you had MoM with Professor X (an ACTUAL Professor X variant portrayed by Patrick Stewart, who portrayed Professor X in the Fox movies), and now confirmation that Kamala's a Mutant and Mutants already exist in the base MCU universe. Next step is to slowly introduce X-Men characters into the movies/shows before the actual FIRST MCU X-Men movie.
If we do get her as the sort of new X-men member, I still hope they have Shadowcat and Jubilee.
I don't see her as an X-Men character. I think her, Ironheart, America Chavez, and others are going to be the setup for the MCU's Young Avengers. Kamala WILL have cross-overs with the X-Men, though. I think, being the fangirl she is, she'd much rather be a part of the Avengers (Avengers-associated) than the X-Men.