Well, that's a big mistake on your part though, because it depends on where YOU stand where the project will be built. She is just the character to speak to to get things going.
I think she even says that.
It's also not really imprecise. Everything is tied to the invisible grid. You can determine the size of a block by digging a hole or planting a flower or dropping an item on the ground. It will occupy exactly one block. A rock occupies one block. A tree occupies one block. There is a maximum of one weed per block. Clovers are one block big. And so on.
Also she doesn't talk too much. That annoying HHA weasel/otter/beaver/whatever in Nook's Homes talks too much. WAY too much. That's the guy who you should be annoyed of.