Assuming your FRA start of benefits at Sep 2016, and spouse's birthday in Jun 1951, the SSA has on-line calculator at
https://www.ssa.gov/OACT/quickcalc/spouse.html that "will tell you the effect of early retirement on your spousal benefit as a percentage of the worker's primary insurance amount"
Using the info above, it says:
"You choose to receive benefits 9 months before normal retirement age. Your benefit will be 46.88 percent of the worker's primary insurance amount." So the "penalty" is 3.12%
" You" in this case means the spouse. So if yours is $2100, hers should be $984.48