Think you and your stepmother are confusing various retirement systems. I am going to try and clarify what is going on, but a lot more information would be needed to actually determine causes and effects. Please note I am not a human resources professional but am familiar with the government retirement pension systems (CSRS and FERS) and a bit with Social Security as well. What you are highlighting is a complicated benefits case that may involve CSRS and Social Security, and possibly another state-run retirement system's benefits.
First, you state your Dad was a 32 year federal employee (GM/GS 13). Given number of years in service, he was probably covered under CSRS and did not contribute to Social Security as a federal employee. Most likely he had few if any covered Social Security wages. The check your stepmom is receiving is probably survivor's benefits from the Office of Personnel Management (OPM), which administers CSRS and FERS. You need to confirm exactly who is providing the pension fund check before drawing any conclusions.
Secondly, you mention your stepmom worked as a Deputy Sheriff. In many states, they did not contribute to Social Security either, and were in a state-run pension plan. You need to confirm whether she, in fact, contributed to Social Security. If your father had at least 10 years' covered SS earnings, a widow's benefit could be paid at age 60. That benefit amount is unchanged at age 62. The only way this benefit would be reduced is if she receives a non-covered state or local govt pension, based on her own, and not your father's earnings. Until you know actual source of her own pension, it is not clear that Social Security is the culprit for the $100 estimated reduction at age 62. However, I do not know OPM rules enough to know whether she might suffer a reduction for some reason under CSRS. Who said and how was the estimated reduction of $100 computed? Based on the info you provided, my inclination is to believe it is not an SSA-imposed reduction.
Third, several folks alluded to the earnings test. This applies to wages, salary, and some business income as a result of active participation in a business. Pensions don't count for earnings test purposes. If you exceed the annual earnings limit, then your SSA benefits are reduced. However, you gain parts of this reduction back at full retirement age. Go the ssa.gov to determine your stepmom's full retirement age. Social Security increases may offset a widow's pension by 2/3's of any noncovered pension based on your stepmom's own earnings. For there to be a $100 reduction, her noncovered pension would have to go up about $150. If her own pension is based on covered SS wages, then there would be no reduction.
As you can see, this is a complicated matter. Go to SSA.GOV and read the publications there. Before you go there, make sure you know the exact sources of the retirement pensions discussed here. Who pays them is critical to understanding any SS rules that had to be applied.
SOAPBOX: Remember your US representative and US Senators all made the rules this complicated. SSA and OPM merely execute the rules Congress passed. If you want them changed, communicate with your elected representatives.