a real bitch because of the chafing

[Pavel Pin]

Amy says to Aubrey that she has been hiding from her dad:

Aubrey: Why are you running from him? I wish my dad would pay attention to me.
Amy: Because my dad wasn't a very nice man. So, when I was 18, I had to run away, which was a real bitch because of the chafing.

How is "chafing" related to "real bitch"?
Source: Pitch Perfect 3 (2017)

 

[Thomas Tompion]

I think to be a real bitch here means to be very disagreeable, and maybe chafing means teasing, or criticism.