...Why? We hold blood drives for blood giving. Why can't vampires survive off that? There's plenty of ways to get blood that don't involve non-consensual acts or murder.
EDIT: After double-checking, I also don't see where it says only human blood, meaning she can survive off the blood of animals. Meaning that livestock takes on double value if they serve the meat to humans and blood to vampires. There's ways around this roadblock.
What's more, she clearly fed on the blood of the orc that attacked them, further proving that she, in fact, is not dependant on human blood but can in fact feed on the blood of pretty much any living being.
The main difference in here with the demons from Frieren, is that demons are explicitely stated to be monsters devoid of the actual concept of emotions humanoid have, and have in fact evolved in the forms they have as mimicry to more easily approach humans, their main source of food. Demons in Frieren are fundamentally different from vampires in this story, from what we can see so far.