shutoff valve is.  Turn off the valves to your faucet first, then turn on the faucet.  If the water stops flowing, then there is really 0 risk in doing it yourself.  If that doesn't stop the flow, then turn off the whole house water first. (replace the faucet valves at the same time).

This isn't that difficult.  I replaced 2 faucets this last year... we just wanted an easy one for the children to turn on and off.

As a side note, some women grow up in homes where the father literally has messed up so manhy projects that their mother always insisted on the professionals coming.  It may take awhile until your wife realizes that her life experience expectations need to be adjusted.