Question: MacBook Pro Retina mid 2012. The error "No connected camera" could be "solved" by "sudo killall VDCAssistant" years ago.

Today the error comes again but VDCAssistant cannot be killed. I have restarted the MBP several times but no luck.

The camera works if I login High Sierra with another (admin) account.

Question: how to make it work for my daily account?

Answer: 
Sounds like a conflict with something that is running in your personal account. 

Try logging into your account holding down the shift key. Hold it until everything has settled, it can take a minute or two. This will prevent login apps from running. 

See if the problem remains.
If it works in other user spaces, just not in yours, it may be tied to the parental controls which includes a camera exclusion. I would check the System Preferences / Parental Controls and see if there is an anomalous toggle on "Allow use of camera".