ya that has happened to me also before just double check all the characters of the pin. I have accidentally put like 0 instead of o before or 1 instead of I then it wont work (obviously). Scanning the other persons barcode is the easiest way to do it to make sure that its right.
Edit: well you answered as i was typing my response haha well then im not sure why its not working if you are sure its right. All i can say is try scanning their barcode though bbm?
Have you tried adding her PIN to your address book, then just sending her a PIN message (outside of BBM)?
If you are on different carriers, have you made sure your @carrier.blackberry.com e-mail addresses are in your address book? You should be able to then pull up each other from the address book entries (from within BBM) and add the person. That should (hopefully) get around the requests going to never=never land.
The last thing to do would be to see what OS she has on her phone. If she is running 4.5.0.131 or newer, she can update to BBM 5. She could also update her phone to the latest OS if she is still running 4.3. That would give her BBM barcodes and such.