Retroactive laws tend to be problematic. I will bet that her attorneys will argue that the law violates the ex post facto prohibition in the constitution, so she should not have to pay. We’ll see.
Feds had no problem passing the Lautenberg Amendment that denies the ability of people convicted of misdemeanor domestic violence to own firearms, even if conviction was 30, 40 or 50 years prior to bill passage.
That law is an interesting debate. Sorry... off topic here.