In order for Karryn to lose virginity in gloryhole you will have to use pregnancy mod made by
drchainchair2
From what I've seen, developer made it possible to have all sexual skills unlocked during gloryhole event without actually getting them through normal way. Do check the CC_Config in plugins folder and read carefully about various tweaks.
I haven't had a chance to test how it works, but since it's a mod, do not expect any special lines about Karryn losing her virginity.
Edit.
I'm actually retarded, because I didn't read the question to the end. It's totally safe.
Edit 2.
Correct me if I'm wrong, but running out of stamina and energy will trigger a level 2 lose scene, so not entirely safe.
No clue, if inmates can break in during the event and trigger fight or lose scene.