<<So the company's HR department got an Email from Carrie@Jobnet with nasty stuff about you? >>
Thats exactly what it sounds like.
Here's my question, are you sure these attacks are personal towards just you? Ask her if it's happen to anyone else. Since the company is actually based out of WI, someone would have to go to some trouble to find out who you were using for a employment company since it's not local. Can you think of who you have told that you were using that company? Otherwise how would anyone know? IS there anyone you've pissed off lately who has seems to have hacking abilities?
I'm with LANMAN, get a real email account. Your ISP should give you serveral emails, so create one you can use solely for this. Just use some form of your real name.
Also i'd try to change the password to your email account and have her do the same.
Have you scanned your computer for all trojans and key sniffers? I know this sounds silly, but it's worth a shot to be sure someone doesnt have access to your computer and can see your files, then spoofs her email and sends out emails about you. Just a long shot.
I'd definately change your password ASAP and quit using a web based email.
Next step, call the FBI and have her forward the email to them.