"In a contest of who's-got-the-biggest-balls, all of you listeners should know Jessica wins." - Hannah Baker describing Jessica after having coffee with her.
Jessica is new to town, but she's not your typical wallflower new kid. She's bolder and more aggressive than Hannah. Unfortunately, Jessica is also pretty violent. This is where Hannah's story starts to get all tangled up, soap-opera style.
After Alex Standall's pits the two girls against each other, Jessica accuses Hannah of stealing her man. When Hannah denies it, Jessica says, "'Hannah […], I know the rumors'". Then Jessica hits Hannah, apparently embedding her fingernail in Hannah's forehead and leaving a scar.
This is some pretty hefty symbolism here. Jessica's violence has left a physical scar on Hannah's forehead, which seems to represent the emotional scars that Hannah clearly lives with as well. For more on this, check out our section on "Symbols, Imagery, Allegory."
This combination of violence, public humiliation, betrayal, and the loss of even a casual friendship with another girl weakens Hannah and contributes to her alienation. But Jessica's story and her importance in Hannah's life don't end here.
The Bedroom Incident
"Cassette 5: Side B" is dedicated to Justin Foley, but it also features Jessica. Hannah doesn't mention Jessica by name in this tape; it's Clay, who saw Justin and Jessica together at the party, who gives us her identity. Other than the people involved, the other listeners won't be able to identify Jessica.
Here's the thing: Jessica will be able to identify herself, and these tapes might be the first time she's hearing about her alleged rape. Couldn't Hannah have told Jessica before, in private? This is an incredibly sensitive issue, one which will be very personal and traumatizing to Jessica, and Hannah may be making things worse. Especially by not acting immediately so that Jessica could get help.
This tells us even more about Hannah. She is clearly in no state of mind to be sensitive to others. Her own inability to deal with her role in Jessica's possible rape is a big part of what drives Hannah to suicide.