I could be totally incorrect, but I thought ng worked as a home health cna. In a home setting it is not unusual for a cna to fill a pill box for the patient. Elderly patients have trouble reading labels and opening the pill bottles at times. This would give her some access. I more believe that she was working to bring in income (with a baby on the way), and as a form of redemption to her demented mind.
As for the pill bottles in the home, I am sure Patricia was on medications for her "dementia" also. That would account for some bottles. Also the 911 calls states she was having trouble breathing. Possible COPD, emphysema?? Those would require meds also. I would not be at all surprised if all three of them were on medi-cal or medi-caid and I am sure that ng was being paid to care for her mil as there is a federal program the state of CA has to provide for family members caring for other family members.
Don't overlook the possibility that there was a practical motivation for that career choice. It would have allowed her access to health care information/training and materials, both important aspects considering that they were raising a secret family in the back yard.