I wouldn't describe it as either an imaginary or virtual person. Given that Rachel is an adult, that would give the impression that you think she’s a bit off mentally.
All she's doing here in this scene is practicing what she's going to say when the guy she's interested in shows up. It's a very common trope in sitcoms and dramas; it's a way of letting the audience in on her inner thoughts. If you want to emphasize that she was practicing outloud when no one was there, you could say something like, "Rachel was practicing outloud what she wanted to say while no one was in the room with her."
To say in this context that she was talking to an imaginary individual would on the contrary convey that she somehow thought she was interacting with someone else in that soliloquy.