I don't have a source but I hope to point someone to one. I'm in the middle of a house move and all my books are in storage so I can't access it at the moment but I think At The Tomb of the Inflatable Pig by John Gimlette states that she died on a forced march from Asunción after the trial at San Fernando. It's not an academic history book but Gimlette gives a list of sources.

Apologies if my memory is incorrect.