I approached the corpses and the elves became threatening. I dispatched them. Finishing, I looked around for more flowers, to my surprise Gerdur was dead in some bushes.
I thought she never left Riverwood?
Do you have any mods that revamp NPC schedules? Immersive Citizens: AI Overhaul for instance has some NPCs occasionally visit nearby towns and whatnot. If not, then I have no idea why she would leave Riverwood.
Gerdur DOES leave Riverwood occasionally. I followed her one time just to see where she was going early in the morning. Anyway, she walked up the mountain at the back side of Riverwood, up past Helgen to near the Stormcloak camp[, then she came back by a way that would take her near to where you're saying you found her.