Thanks for the condolences, everyone. Melodee was about 6 years old, so we think it must've been old age. We kept her as comfy as possible, setting her in a safer spot than right in front of the coop door, putting food and water within her reach, etc. In the end, it was just her time.
Silvie is doing surprisingly well for being the last hen standing. She doesn't seem to be very lonely. There are a bunch of little birds that hang around the coop and run, eating what the girls didn't eat, safe from the neighborhood hawks. Maybe she's adopted them as her flock.
I'm sorry for the loss of your hen Melodee. I have my first small flock and just love them. They are a barnyard mix, but my rooster has the fluffy cheeks, beard, and slate legs of the Ameracauna. I hope Silvie is still doing well.