Have to agree this is a bureaucratic problem. Consenting adults. Should she be fired? Yes, definitely, not a question. Her punishment honestly should only affect her education status. Even prohibiting her from any future educational position is fine with me.
But prison time? If anything maybe a few months, but this is not a dangerous person so she shouldn't be in a prison. The only danger she presented to society was within that of an education institution, so simply do what is necessary to prohibit her from such a situation. Why are we sending this person to prison???
Ask yourself what the purpose of prison is before you engage in any form of bureaucratic dogma.