When a peace-seeking alien crashes in remotest New Zealand, a feisty female scientist and a taciturn hunter must rescue him from a war-like Vietnam vet.

Seismic activity aside…

As Knightrider and DPG pointed out, it’s hard to figure out who the MC is – who’s story it is. You describe four characters in the logline all of whom may be vital to the plot but it isn’t clear? how.

I think one of the biggest problems is the descriptions you’re using:
How is the hunter being taciturn relevant? Could you use a more common word than taciturn, such as ‘shy’ perhaps?

What does “…war-like Vietnam vet…” mean? Is he or she a Vietnam vet or not?

Why do you need to specify “…female…” as part of the MC description? It’s unnecessary as it contributes little to the reader’s understanding of the plot. If you want to specify that you’re writing a female lead character, use ‘she’ or ‘her’ in the logline. Otherwise, it seems more like pandering to a trend than a genuine need of the story. Women and men are equally capable of fulfilling the role of a main character, specifying one gender and not the other (you didn’t use ‘male’ for the hunter, vet or alien) suggests that you’re trying to make a point instead of telling a story.

Once the descriptions are adjusted the causal connection that binds all the characters together may be clearer.