This is when they introduce the secret society of mostly fox and raccoon yokai that have monster doctors, that somehow also are in plain sight due to illusions
Given that she was a child when her mother died, and is the last of her kind, it's not at all surprising that she has absolutely no idea how long a pregnancy would be, even setting aside how things work when it's an inter-species relationship.
The rabbit and cat would probably have a vague idea, at least.