Hoping someone can help me find this book! I read it in the late 80s to mid-90s, and it follows a girl (Megan?) and her mother over a few days when there is a real risk of a nuclear war between the US and the USSR (like the Cuban Missile Crisis, but in the 80s/ 90s).
I think they lived in California but somewhere fairly rural/ isolated - possibly the mountains. The girl’s boyfriend stays over one night and they might have had sex for the first time. There might also be a scene where they see a flash in the distance and think a bomb has been detonated.
I also think that the end, when the crisis has passed, she says something like ‘Let’s make a baby’ to her boyfriend but doesn’t really mean that she wants a baby, it’s just an expression of having a future again.
Haven’t had much luck on Google as it just brings up post-nuclear war books (Children of the Dust, Z for Zachariah, Brother in the Land etc). Feels like a very long shot but maybe someone else will remember it!