I believe it’s exactly that :) although I am wondering the same thing :0
A Banma means that you have two kind of mana, I think, and so it's a bit fragil, because normally those two types of mana are opposites, so her mana has to have an equilibrium so thay it doesn't go out of control. And yes she is a Banma bevause she is half angel, half demon. Btw, I don't think to be a banma you have to be half angel half demon, you simply have to have two types of mana or something like that living in you.
Currently Rin is in a state where there is a balance between Demon and Human blood flowing inside her. People like Rin are called Banma. In saying that her Demon blood will eventually eat up the Human blood. This is all explained in chapter 24. Banma is born from a demon and a human. Sein, Rin's Mother is a Paladin she is a human. She is not an angel.
But I think Rin's Mother's Companions have wings, so doesn't that make them angels?
I dont know maybe, despite that Rin's mum was still human and had Run as a human. Rin's mother became an angel being after she died.
Hey, guys. What's up with this banma thing? I don't really remember this being explained before... is this about her being mixed?