Might sound a bit odd, but when it comes to unrequited love, there are usually power dynamics in play. You act differently around this person, you want to get her attention. Not an easy thing to hear when you really desire someone, but often this unrequited desire can only serve to make you feel the distance between you even more so, and then, to idolise her.
Perhaps the best thing you can do is examine your attitude and make tweaks to it. This is a kind of indirect magic. Direct magic would be casting some spell on her to make her fall in love with you. That may well be an option, but there are other things to consider first, or as well as, that primary goal.
First, this might sound bleak, but in any relationship, the one who cares the least has the most power. So aim to expand your horizons. What would make you focus less of your attention on her? Find a hobby you’re passionate about and can pour time into. Start playing a sport. Expand your magic to look to meet other women.
Again, this is probably going to sound like utter bullshit to you if you’re in love with someone, but once you realise there are other amazing women out there (whether you choose to pursue anything with them or not), it will make you feel more secure. It will remove that feeling of “my life won’t be complete until I have her”. Or you might be reading this thinking “but I don’t really want a new hobby, I just want this girl, and any magic seems pointless if it’s not directed at that specific goal”. At this point, you have literally nothing to lose, and it’s not going to harm you in any way to find other things to take up your time and mental energy.
Many women, if they sense this attitude of “I must have you, nothing else matters to me”, it can repel them. If you have nothing else going on in your life besides spending all your time pining over someone, then what would you actually have to offer them if you caught them? Emotionally healthy women are not sexually attracted to servility. You need to have more to bring to the table than just “I’m attracted to you”.
So, work on your own attitude here. If you feel like you MUST have this person or your life is meaningless, and you only want to devote all your time and attention and energy to thinking about her or how to get her, you are inherently devaluing yourself. Focus on what is good about you, and expand those qualities in yourself. Make yourself the kind of person any girl would be happy to have as a partner, by pouring some of that time and care and attention and energy back into improving your own life.
Two outcomes here – either she notices, and is impressed, and decides to give you a chance, OR you find that your own life is now so rich and fulfilling that your attitude towards her changes, and you see her as just one of many options out of the multitudes of people who could be well-suited for you.
Also my apologies if any of this comes off as harsh or me making assumptions, but just wanted to give you something to think about.
If you want to work with entities to help you here – as far as demons go there’s Belial, to help you take control of your own life; Sitri, to help you “exude an aura of lustful power”, Cimeries, to “remove subconscious fears that weaken you”. There are various other angels and sigils and spirits that can assist you in finding your gifts and talents, in being motivated, in becoming confident, and so on. If you specifically want to remove your feelings of love for her I’d look at cord-cutting rituals, a freezer spell on your own emotions, or contacting an entity of love like Sallos or Archangel Haniel to ask them to remove these feelings from you.