Health, you said: She gets paid per patient ... Who pays her? Your Group? Or the insurance carrier? The answer to who pays her? will determine what my answer to you should be.
It sounds like you are discussing a Group practice, and the legal entity that is the Group has a Group NPI. It sounds like any billing would require the Group NPI (Type 2 - who gets paid) and the individual practitioner NPI (Type 1 - who did the work). I am assuming this is the case in your situation, so here are a few points to consider, based on my assumption.
If this collection of workers meets the CMS definition of "Group", then payment may not be sent to any individual practitioner within the Group for work done under the name of the Group. Payment must be sent to the legal entity that is your Group name. Payment for the charges goes to the Group, and the Group pays the individual practitioners / subcontractors for work done under the name of the Group. (Note that, if the Group allows a practitioner to work outside of the Group name, this restriction is not in force for that work done outside of the Group.)
Also, for a collection of workers who meet the CMS definition of "Group", no individual practitioner within the Group may be a participating provider in an insurance carrier plan - while working for, and being paid by, the Group. Rather, the participating provider would be the legal entity that is your Group name. (Note that, if the Group allows a practitioner to work outside of the Group name, this restriction is not in force for that work done outside of the Group.)
A nurse practitioner, and maybe a lcsw, can do business in their own name, just like a doctor (assuming certain conditions are met). In this situation, the Type 1 NPI (who did the work) and the Type 2 NPI (who gets paid) on the billing document would both belong to the nurse pratitioner or lcsw. I know that at least the nurse practitioner will get paid less if s/he bills in her own name this way. Which leads at least the nurse practioner to often bill under her employer's Type 2 NPI (who gets paid), while providing her Type 1 NPI (who did the work). Her employer gets paid at the higer rate, and turns around and pays her. The amount the employer pays her is up to the employer.
In your situation, it sounds like the employer of the lcsw is the Group. If your setup meets the CMS definition of "Group", then your Group is the participating provider in CIGNA and United Health Care - not the individual practitioners. Your lcsw would do the work, and a bill would be submitted to either CIGNA or UHC with the Group's Type 2 NPI (who gets paid) and the lcsw's Type 1 NPI (who did the work). Because the charges are being billed in the name of the Group, and the insurance carriers would recognize that the Group is a participating provider, the charges would be paid at the contracted rate. This is the required configuration for billing unless your lcsw is authorized to bill under her own name. But, if your lcsw is being paid for her work by your group, she is not allowed to bill under her own name even if she is authorized to. Billing under her own name would cause payment to go directly to her, and not to your Group. And if your Group is paying the lcsw for her work ... and she gets the money from the insurance carrier instead of your Group getting it ...
The fact that your lcsw is not credentialed with CIGNA or UHC would be an issue only if she were billing under her own name. Since she is being paid for her work by the Group, she should bill in the Group's name, not her own.