Tonya,
Social workers are not too difficult to bill for. With your experience you shouldn't have a problem. You understand insurance, how it works, and how to file claims, now you just need to educate yourself on mental health billing. There are only a few CPT codes that social workers use, and the icd-9's are the same, just that you will be in the 29x.xx to the 31x.xx range. You need to understand auths and referrals and a few other small things.
As for software, any good billing software will work for social workers. You don't have to have one that is specific to mental health. There are some specific ones out there, but I personally don't have any experience with them directly. We have billed for mental health providers for 16 years. We use the same software for all providers.
We do have a book on billing on billing mental health if you feel you need more information. You can view it at:
http://www.medicalbillinglive.com/mental-health-medical-billing.shtmlGood luck!
Michele