Yes there are multiple ways that ipv4 can be translated into the ipv6 range. That's not what I'm suggesting here. I'm suggesting the existing ipv4 assignments to natively work in ipv6.
This means she'll have to either send an IPv6 header or an IPv4 header with a false or blank IPv4 from address. If she sends an IPv6 packet, Bob's IPv4 network stack won't be able to understand it and drop the packet. If she sends an IPv4 packet with a blank or false IPv4 from address, Bob will receive the packet, but won't be able to send a response.
Generally, if it's not being routed right now on the public internet, and just used inside networks for migration purposes, it's not as useful for the "my Minecraft server has this IP" use case.