I think you have to realize that professors get bullshit excuses all the time.

Your power went out and you can’t take the test? Sure, easily verifiable.

You also lost cell service? At least in the US, Cell phone towers are required to have emergency backup power for situations like this, which is why cell phone service usually persists during an outage. Unless there’s a fluke with the backup power or we’re talking a big hurricane level storm. Which happens. But… I’m starting to doubt your story.

Your gate is electric and solar powered? How is this relevant?

How would you have contacted her even if you could leave? By driving to a library which… probably also doesn’t have power if the storm was big enough to take out your town’s cell tower?

We’re you going to drive to the school and knock on her office door when… the class is online?

Now I think you’re making stuff up. And that’s probably way your professor thought too. And they don’t take kindly to being lied to.