Rekki Lune is definitely one of the strongest people in her world. I'd put her approximate power level on par with a mid-tier Marvel character. She definitely couldn't take somebody like Thor, Superman or Goku.
She can do stuff like this:
and this:
And of course, this:
She has almost endless stamina, she can jump really high, throw a car and survive and keep fighting with a bunch of broken bones.
....Unfortunately these things, while handy for fighting demons, don't really help with her real problem of being stuck working for an even more powerful magic king who treats her like dirt.