There is no rule stating that you have to wait any period of time before petitioning for your new fiance. However, USCIS may question the validity of your original marriage given the timing of your divorce and the suddenness of having a new girlfriend. You should speak with an immigration attorney to ensure that your fiance is otherwise eligible to adjust her status and that you file all of the proper paperwork.
P.S. You cannot petition for a "girlfriend" unless she becomes your fiance or wife.
DISCLAIMER: This answer is provided as general information, which may not be appropriate for the specific facts of your particular situation. No attorney-client relationship has been established based on this limited communication. You are advised to consult with an attorney in your jurisdiction before taking any action or inaction that may affect your legal rights. www.hecklerlawoffice.com
I agree with what the previous attorney stated. Though there is no time period that you need to wait before reapplying, the validity of the first marriage will be called into question, and potentially make the petition for your girlfriend look suspicious. If your girlfriend become your fiance, you will need to be able to prove that you are BOTH legally able to marry - so your divorce would need to be finalized. I would strongly suggest you speak with an attorney about this issue.