Its likely going to be very hard to prove and will amount to nothing - but it'd be interesting to see what would happen if this is true. Milei and his sister have a weird relationship (in Argentina they often joke about them being a couple) so it's unlikely he'd throw her under the bus. They'd need to find a way to spin it, and the situation is not looking good.
But as I said, this will most likely amount to nothing and we'll be talking about somtehing else next week. This is the Argentinian way!