If she provided her correct Social Security number and filled out the VA forms correctly, she shouldn't worry about the money she has already received. But there is no guaranty that she will continue receiving the VA pension amount, even though no new law affects these particular pension rules.
From your father's history and the amount she is receiving from the VA, it sounds like she's getting survivor's benefits from what the VA calls a "Wartime Service Pension." This can be paid to the surviving spouse of a veteran who served on active duty during wartime. But this particular VA pension only goes to a surviving spouse who has low income, including Social Security benefits. The amount of allowable income, which changes every year, is quite low but does not count as income amounts that have to be spent on medical care. So, when your mother first applied for the VA survivor's benefit, her income, minus her medical expenses, must have fallen under the line to qualify for the pension. However, if her income (minus medical expenses) later climbs over the yearly allowable limit, she could lose that pension.
You can find the specific rules of these survivor's pensions, and how they calculate yearly income and pension amounts, by going to the VA's special web site page on spouses' pension benefits.