How do I get Gleda the Goat to stop trying to kill me?

I just tried this on my own game to see how you could get around it. After killing the giant I unloaded a bunch of Lightning Bolts into her to get her really angry.

All of Calm, Pacify and Harmony worked on her and caused her to become passive again (she's only level 3, so even at very low levels Calm should work). I also found that simply putting my weapons away caused her to become passive again as well.

Speculating, but the Imperial racial power Voice of the Emperor probably won't work as it only states that it affects Humanoids.

Disclaimer: I used a modded PC Legendary Edition client to test this, with all of the unofficial patches installed. It shouldn't cause any difference but there's always the possibility that it might.

Try to reload any save before you attacked the goat. Then try to kill the giant without touching the goat, and then go back to Rorikstead.

You could also use a Calm Spell too. If you don't have one, they can be bought from any mages.