^I prefer we not question the morals of the individuals, or their reason for wanting to perform any operation.
That said, I would advise you get a candle, preferably black, though any kind of candle will do, an altar if you have one(and you do not need one for this spell), and a taglock/fetish link to the target. I assume you know what can be used, and I will only mention that the closer the taglock is to the person, the stronger the connection.
Before the ritual, I would suggest consecrating it to connect to the person.
1. Go into trance, and mentally reach out to her energy, pulling it in with each inhalation, and into the object with each exhalation.
2. Slowly place the energy into the object, through your breath, until both hands are clasped tightly on it. Visualize the force entering the object, expanding, and "clicking". Feel the power flow in your hands.
3. See it as being ''sealed'', and activated. Verbalize your intent, to make that fetish link that person, and you are good to go with it.
Perform the ritual at around three in the morning. The main reason is obviously what most will mention, that it is the witching hour, and all the spirits are more active, the veil is thin, blah blah, but there's also the fact that the victim is likely asleep, which means their defenses are down and they're unconscious, meaning most susceptible to magical influences.
Sit there in the darkness, meditating, and when you feel it is time, light the candle. Gaze into the candle, letting it sink into your mind. Gaze into the blue part, and breathe, furthering the meditation, furthering the trance. See the fire burning away the skins of mundane existence, until all that is left is magic.
Hover your hand above the candle. Close your eyes, and visualize your intent, whatever you want them to say/do just see them doing it.
Now, add emotion to the operation. Emotions are a fine thing to have, attachments are not. Exhaust all your desires in this. An important note here is that you must not only visualize how you would feel, but actually attempt to feel it. See how HAPPY having that result would make you, the RELIEF it would bring you. Push that into your right hand, all of the raw WILL just overflowing from the fetish link, and into the candle.
In the candle see her, lying in her bed, sleeping, or if she's not sleeping doing whatever. The visualizations here should come on their own. See a cord tying her to the gateway you have opened through the flame. Just keep pushing, just keep directing your will, through the candle and into her.
Simple, RAW desire. So much of it until you are exhausted mentally. Once you feel that you can't WANT it anymore, verbalize your intent. In the present tense. Gaze into the candle, wish it once more, and blow the candle.
Inhale the fumes, put the things aside, write the experience down if you keep notes, and go make yourself a sandwich or something. Watch a movie, do anything that is going to ground you back into this world.
FORGET that the ritual ever happened. Do not think about it, do not repeat it. If your mind happens to stray towards the operation you've performed, substitute any thoughts of doubt, with elation at having it happen. Simply put, substitute any emotions that may be counterproductive.
And wait for it to happen.
If you don't get anything, check if the magic is working, via divination, and if all seems in order, continue your non-attachment thing. It will happen.
If you do not get a sliver of a result within a month, only then can you even consider the possibility that it failed. After that divine on it, or look at what went wrong. We can help troubleshoot.
So...how does the spell work?
Well, it's a taglock, connecting you to the victim. In consecrating it, you're forming the connection. In meditating in darkness you are both meditating and connecting to the currents of black magic.
Lighting the candle and engaging a trance means you're simply shedding normalness in favor of magic. It helps you slip more into the trance. Furthermore, fire is one of the three natural gateways connecting this world to the astral. By focusing your intent into this, you're focusing your will into it. By projecting it outward, you are basically pushing it out, and by connecting to where she is, you are opening a portal on her end, and pushing it into her.
I've mentioned already the significance of the Witching Hour, and her likely being asleep at the time. Saying it out loud, helps seal it into the world, and releasing it to manifest.
As for the ''forget about it'' part, that's the same reason so many spells have that ''don't look back'' clause. You're basically releasing your intent into the universe and not worrying. Worry is an emotion, as is doubt. They create negative thoughtforms or vibrations that interfere with the workings of the spells.
Even if you're 100% optimistically sure, the forces behind the spell, the things which are guiding it, sometimes external, most often internal, would think that you don't trust them and have to monitor them, so instead just forget about it altogether.