I have a theory about her as a human, how she got her powers and how she somehow went to the mortal realm even if normally, Sinners can't do that:

Rosie was once just a human living in a small town, and was a respected member of it. But she discovered witchcraft, and saw it worked. She then got interested in Heaven and Hell, how they were, the people's powers there, etc., so she made a test. She tried to achieve some angelic magic very directly, with magic, instead of spiritually, and she did, she called herself a "Witch of God". So she had an idea, after years, and years of studying occult stuff, she tried to "curse" her soul with a bunch of angelic magic, and she succeeded, and now she would gain powerful angelic magic once she dies and gets in the afterlife. Just some time after all that, a famine, an economy crash, a natural disaster, whatever, hit her country. It became so bad that people didn't know what to do, so they resorted to cannibalism, died, and went to Hell. But just before all the cannibalism stuff, she made deals with all or almost all (atleast many) of the people in her town to sell her soul to her, and in the afterlife, they would become a united colony under her as the leader, with her protection and a united, strong collective. She went to Hell for:

1. Witchcraft
2. Engaging a lot with holiness magically, not spiritually
3. Soul deals
4. Cannibalism

So, overall, that's why her energy is golden and she's so powerful (enough to easily make Alastor the strongest Sinner in Hell, beside her), but her energy isn't of a pure gold color, because its corrupted by her being a sinner and her being in Hell. But, you may ask, "How did she go to Earth if she's a Sinner?", well, as I mentioned earlier, I also have a theory on that. She can do it because she's powerful enough to partially break the Hell-Earth barrier for Sinners. Let me explain, basically, I theorize the angels put up an invisible barrier that violently repels Sinners if they try to get to Earth magically. But it's flawed, because, first of all, they underestimated Sinners, second of all, they didn't want to "waste their power" on this. So Rosie managed to break it with her power, that is much more powerful than one of the average Overlord, but only partially. The barrier still blocks her from manifesting her full form, so she only could manifest her voice and energy constructs (moving tendrils with hands, in Alastor's case) that are strong enough to physically, comfortably interact with the Mortal Realm, and they have to be formed from an anchor (a radio, in Alastor's case). 

So, that's my theory, what do you guys think about it? Let me know. What do you think I should add or remove? Is this a crackhead theory or a good theory? Idk. Just let me know. I hope you enjoyed reading this!

So, I have a theory about Rosie.