Wiki Billing for Behavioral/Mental Health Counseling during a well visit.

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My practice is going to start billing for our behavioral health counselor in a few months and I'd like to get some input on how to appropriately bill for her services during a well visit.
For example, I have a 99394 for the well visit and she provides 15 minutes of counseling during that visit, what would be the most appropriate ICD-10 and CPT codes to use along with the 99394?
I should also mention that we bill Medicaid and CHP only.
One of my providers asked about using Z71.89 as the ICD-10...?
Thank you in advance for your input and help.
Its really going to depend what this behavioral heath counselor is and what they are going to do. Possibly 90832 is spending at least 16 minutes, possibly 96150-51