If this came on relatively suddenly then it is probably less likely to be internal laying but possibly salpingitis (infection of the oviduct)..... that hunched lower back suggest it or perhaps Fatty Liver Haemorrhagic Syndrome causing a sudden and
severe case of ascites, which is putting pressure on the heart and/or respiratory system.
Sadly I would agree with @lazy gardener that it would be kinder to end her suffering now as there is nothing you can really do for any of those ailments at this advanced stage other than trying to drain which might only buy her a little time anyway.
Would you feel able to open her up and see what the problem is after you euthanize her? I would be interested to see photos of her internal organs and read what you find if you are not too phased by the idea. It can be beneficial to learn from these sad events by improving our knowledge.
severe case of ascites, which is putting pressure on the heart and/or respiratory system.
Sadly I would agree with @lazy gardener that it would be kinder to end her suffering now as there is nothing you can really do for any of those ailments at this advanced stage other than trying to drain which might only buy her a little time anyway.
Would you feel able to open her up and see what the problem is after you euthanize her? I would be interested to see photos of her internal organs and read what you find if you are not too phased by the idea. It can be beneficial to learn from these sad events by improving our knowledge.