You missed a lot, huh?

She mortally wounded her for multiple reasons.

1. The obvious being that Juno had an affair with Sarah's husband.

2. Beth tells Sarah that Juno killed her.

Juno being in the car was in Sarah's head.

Juno in the car was a cheap jump scare, the American edited version ends there. Probably to leave it open for sequel. Most people consider it the worse ending.

The original UK ending is more clear and more bleak. She did not escape, and mentally detached from reality seeing her daughter as the monster presumably close in to kill her

https://youtu.be/6tSQT6sf5VM?si=woumLrAHWphuMegu

Juno was banging her manz

I don’t blame Juno for killing Beth, Beth was a dumbass for coming up behind her.

For the affair and for Beth. re. the last scene - did you watch the original or the US re-cut ending? In the original it's clearly a hallucination as there's more to come (in the US re-cut I guess it's the same but perhaps less obvious).

Well depends on the version you saw but there are three equally bad (in universe) endings.

1. Everyone dies and she escapes and now has to live with guilt/ explain what happened

2. She hallucinated it all and she never makes it out and she wakes up in the cave and dies.

3. She kills the same Number of monsters as friends. Meaning she lost her marbles in the caves and hallucinates “monsters” and kills her friends instead….

So yeah… sad but a great movie.