If he is filling out her mail-in ballot, then when she signs it, it should indicate that she’s voting with her own free will, under penalty of perjury and ballot fraud.

Later, if it’s determined that he coerced her into signing a ballot that he filled out, he can be charged with fraud, and she can be charged with perjury.

And then prosecute every single instance of it. The real problem in America is that too many people think that everything is legal unless they arrest you for it. It is the core philosophy of MAGA.