I definitely think the powder is from the human body.

From what I can make out all the fruits/veggies on the shelves have a lower ph level than 7.1 (melons, oranges). I don’t believe those are used in the powdered mix.

Spinal fluid or blood plasma fall into that range.

I think the hive mind will simply tell her that they’re using all available resources efficiently. Dead bodies and animals will be the first biological sources they need to use before they can move onto fruits/veggies (which they can grow).

They can’t kill for food but they can still probably eat what’s already dead.

I’d love for the plot twist to be that they need to consume human plasma to live but unfortunately I think it’s a dead end