Depending how flexible the routing of the Gina is, you may be able to do it without a mixer. If you can route the input of the gina to another output of the gina, you could send that out to the reverb box, and bring it back in to another input, and monitor the verbed signal. Again, I don't know if the Gina can do this, but maybe.
A mixer would be the most flexible route. You could send an output of the gina to the reverb and then to a spare channel or two on your mixer. Many different ways to achieve the same thing.