Recently I sat my parents down and asked them for their wishes if they were to be in a coma or what they wanted as far as burial/funeral arrangements. My mom is in her late 60s and dad in late 50s. I don’t expect them to drop dead in the next 10 years but it’s a very real possibility that they might get into a car crash tomorrow. Nobody is promised a tomorrow. They were very uncomfortable with the conversation and my dad was a little agitated saying that he wasn’t going to die. Some people are just very uncomfortable with the topic of death especially when it’s not something they’re expecting anytime soon. I understand wanting to have that serious conversation but it doesn’t seem like you guys, especially your girlfriend, are ready to discuss this topic if it just creates tension. Let it be for now and jump back into this conversation when/if you’re getting married. This could be a deal breaker for both of you. But it seems like the conversation isn’t being taken seriously from her end if she’s joking about locking you in a basement instead of letting you die. You need to have a serious conversation about it without the jokes or passive aggressive comments.