Does CHAMPVA for family prevent HSA?

Yes, you can have an HSA and make contributions to it even if you have VA benefits. Receiving preventive care services or treatment for a service-related disability from the VA does not disqualify an individual from participating in an HSA.

To make HSA contributions you do still  have to be covered under a qualifying HDHP.  

If my wife is covered under CHAMPVA  health care plan only. She does not have a seperate HDHP. Does this mean she is not eligible to contribute to an HSA?

I presume that CHAMPVA is not classified as an HDHP. As such, she would not be able to contribute to an HSA. You might contact CHAMPVA and ask them about HDHP policies and HSAs.