Fantasy read about 4 years ago: starts off in a castle on a desolate sandy land and a girl who is chained magically to a cruel villain, and she can travel through a different plain where souls are lights

[Rains]

It starts off with this girl in a castle, i am unsure if it is a castle run by a King or an evil Lord
The owner of said castle is evil, and uses this girl to fight (i do not remember what), and he also abuses her and punishes her.
Also, the setting of the land around this castle is real desolate, like sandy and dead trees.

She can travel on a different plain, & when shes in this plain, living things are seen as lights
She is wanting to escape but cant as she is chained, through the plain, to the evil guy

Then she meets this guy, who is from a group of people who oppose the villain
This group of people are from a different plain, and they travel to their dimension through a golden river
& the setting of their plain, if I am remembering it correct is a floating mountain, and it has a beautiful castle, and the guy may be a prince, and when she first arrives everyone is super edgy about her being there
I do not remember if they throw her in jail for a bit or fight her, but I do remember that she accidentally found out how to travel their golden river to get to their dimension/plain and the golden river doesnt like her there and she has a difficult time getting out of it

The main girl is supposed to be UNable to travel through their plain, and vice versa, but she is able to travel through both plains (the golden river and the dark plain where only souls are lights

This is also set in a fantasy/dystopian type setting.

I really hope this wast confusing as hell. PLEASE HELP!

[Rains]

SPOILERS


I remember a scene where the evil guy punches the main girl in the face after she came back from a short mission he sent her on to kill someone, and she didnt kill them.
So when she got back he punched her, or something, and she ends up passing out.

Also, I believe she is hiding something behind a dead tree that is in the castle grounds. I think the evil guy is able to get into her mind and see what shes thinking, so shes hiding something in secret when he is not paying attention to her.

Also, I remember a little more detail on the plain that she is able to travel on at first.
Its black and dark, but you are able to see the outline of things, and things that are alive, she is able to see them as bright lights.

When she finds she can travel the other plain, after meeting the main guy character, that plain is traveled through a golden river that almost wants to consumer her as it sees her as evil.
I remember a scene where she goes in on her own, without the help of the guy, and she almost gets dragged under and has a difficult time getting out
Also, if she ends up drowning in this golden transporting river, she will be lost forever.

I believe there's another scene where she is in the world where the main guy character lives, and she is feeling very sad from not being accepted by the main guy characters people, and she ends up purposefully jumping off the edge of her balcony from her room high in the castle, and the main guy character freaks out thinking she just killed herself, which I think was her point, and she ends up finding a new power, accidentally, where she is able to fly as a mist of sorts.

i hope this helps a little more.

[Lobstergirl, au gratin]

Rains, are you still looking for this or did you find it?