Staff discussing money issues with patient

I am a Director at an Adult Daycare and have a staff member who has had several performance issues. The most recent complaint is from a family member who informed me that this particular employee has been asking her mother many personal financial questions.

She asks several times how much money she receives each month from social security, Medicaid, etc.. and asks how much her daughter receives from a pension. Also she makes make inappropriate statements such as "it must be nice your daughter has enough money to quit her job and stay home with you." This family member is outraged because she is a very private person and her mother is not. She will disclose any information this employee asks.

I confronted this employee and she denied it. However, due to the number of other complaints I have a difficult time believing her. My boss refuses to terminate her employment and I am becoming very frustrated beyond belief.

What would you do in this situation? I need advice!!

Thanks in advance!