Everything included in the story must serve the story, with Rachel's death being brought up by multiple characters it sure seems like one person we know is gonna be responsible, it would be a waste if it never comes up again or some rando did it.
I like your Ethan theory, furthermore i'll add that Rachel's death occurs right after we have our fight with him, he was probably stressed out after getting his ass kicked.
Also given his unhealthy obssession with Erynn, he might have targeted the first blonde girl he had at hand as a substitute...and with Rachel not playing nice(aka not agreeing to get fucked in an alley), things might've gotten out of control.
Since you are a new guy to Intertwined, let me tell you that you are lucky, when this scene first appeared the sequence was:
We spot the girl behind the dumpster... chapter ends.
Wait a few months to find out the answer.
Things got pretty wild here.
you forgot she was a camwhore while working as an escort for Ethan!
the girl was working hard trying to make bank...
i wonder if her boyfriend is in prison with a drug addiction...
so she does all she can to try and support him while "enjoying her freedom!"
we see she is a flight attendant, so once a week?
she was also going for a restaurant manager!
i mean she probably didn´t understood what she was doing
but she could just fuck those that understood! its really effective...
So most likely she worked also as a bartender and Ethan aproached her to be a model!
so Also modelling, and thus from there to being a true "escort" wouldn´t be much of a streatch!
so when Ethan finds out she is depreciating his brand by selling it online....