Mysterious weight gain question

[Seneschal]

Well, in my experience she may have a fecal build up, when was the last time she had a poo?

3 weeks ago--She pooed, so I weighed her. She hasn't been fed since then, though, so I had eliminated fecal build up as a cause. She also doesn't have the sometimes telltale swelling above the vent which might indicate the need to pass fecal material.