Ask your neighbour and your landlady to come around for sound tests. What do you all exactly hear? Sometimes buildings just creak weirdly and it's unclear what does and doesn't work. What's no noise at yours is stampede at hers. Figure that out first, also because ventilation can also confuse where noises come from.

It might be that your landlord has to redo the flooring with an extra layer of sound isolation. And you don't have to be particularly noisy for this complaint to be real: moving furniture, like a desk chair, or walking around can indeed sound like a bunch of elephants on a different floor. Wooden floors are very terrible for this noise, but these days they have some awesome vinyl floors that actually absorb noise.

Put the responsibility on your landlady to look for a solution. Perhaps you could put a camera in your main room where you are at night, so it shows what you do normally. That way you have evidence that you're not jumping around.