theres some stuff out there about that..entering into another persons dreams. you do it through a kind of astral projection.
im really sorry, but i dont have the link for it on my laptop
Running a spell like that i think is kind of tricky. spells only work where there is a possibility for something to happen
now it is possible to happen, but someone's unconscious mind is kinda like a mirror. Say for example, you are in their dream...well, its not "you" per se it is themself thats in the dream. A dream is someone's brain talking to itself.
If you have the basics down and know how to cast...i would say come up with your own spell to do this. You know your target and you know your relationship better than anyone else here so i would say a spell like that would need to be highly personalized between you and the target.
Give it a shot and see what happens...it would be great to hear of your success and what you did