Sure, she is afraid of Baam, but she is also a hypocrite and acts as if she did nothing wrong while all the others are wrongdoers. It's implied that she admires Arlen, who is acknowledged as crazy.
So what she says about Baam isn't exactly objective. She kept telling him to stop following her, but once he implied that he would stop, she gave him a reason to pursue him. Why? Ego? Because of her desire to still be precious in his heart? Very likely.
Yeah, Rachel is far from a good person. She does have a terrible personality including hipocrisy and some absurd traumas (like her dislike of her own looks and calling herself ugly: she's normal enough, could even be cute, it's her personality what drives people the hell away), which all have contributed to make her a terrible person who does fucked up things.
Admiring Arlene may hint at such personality having come from long ago. My guess is that she had decided to pursue the same dream as Arlene (watching the stars), and knowing Bam was destined to get in the Tower, she stuck around him despite fearing what he has inside him.
As to your last point, while she goes all "I'm the one that will be the heroine!" She probably acknowledges internally that she doesn't have the power to do it, hence wanting more power and/or Bam to keep following her. When Rachel first arrived into the tower and Headon gave her an unfair and seemingly impossible task, Bam came right after her and passed it, so Rachel "passed" thanks to having Bam following her close. This may have given her the idea that unless she becomes much stronger, she needs to rely on Bam, despite whatever she may think of him
