If she becomes part of your shadow she will drain your life away until you die, she must become your shadow in full and you willingly sacrifice it for her, a replacement if you will. If you try to sever the bond you will die, and trust me it will be far more cruel and painful than you can imagine, right now she is just a normal ghost acting on instinct, or if she is intelligent and manifested her spiritual core to form intelligence she is just feeding on you without true malice, but if you sever the bond she will form hatred towards you. You will suffer so much it isn't even funny, you will have wished she merely sucked out your life energy and let you die.
You clearly aren't part of the spiritual world, the world of aberrations, the quagmire. It will be difficult to find an actual spiritualist who isn't a scammer to exorcize such a weak spirit unless you have $10,000 to pay. Cultivating spiritual energy is difficult in the modern era of pollution and humans are unfit for energy cultivation to begin with, humanity when using spiritual energy will lose whatever they use, and it can take days, weeks, months, or even years to recultivate it, that is why for such a low level spirit you will have no help from a spiritualist, even some of the aberration spiritualists who have been infected and can use negative reiki to cultivate won't both with a ghost at that level, if anything they will aggravate it until the ghost consumes your soul and then exorcise and consume its negative energy to cultivate the aberration they fused with. The Quagmire is a dangerous place for people like you who only have interacted with such a minor corner of it. If you don't want to follow my advice then your only option is spend 10 hours a day in a bright sunny area (wear sunscreen), not in the shade, and absorb the essence of sunlight into yourself, this will replace the bit of lifeforce you lost and will taint you with the aura of the sun, a positive energy that a weak low level ghost will naturally be repelled by. Do this for 2-6 months and the ghost will eventually get so disgusted by you that it will stop harassing you.
However, if you follow my advice and do this sincerely you will become a pseudo spiritualist, you will be able to feed negative energy to your shadow and form a puppet ghost core, which will grant you a healthier body and a longer life, you'll live to 90 at least. As long as you never betray your shadow afterwards your problem is solved. You can return to your normal life. If you wish to step foot into the quagmire then I will give some advice to cultivate your ghost into an aberration and turn that puppet core into a nascent divinity, that way you can become an aberration spiritualist. If longevity is your goal, even the weakest aberration spiritualist lives to be 300, if money is your goal he rich always are looking to employ a being that can kill others with methods science can't explain.
Don't do this halfway, the decision you make now will affect the rest of your life.
