Thanks so much for your kind offer PiddlePod.
I owe you and others an update regarding my Lizzie. I came to conclude that cabergoline was unlikely to help - Lizzie had mammary tumours but no evidence of PT. And while cabergoline might help prevent such tumours, I found no reporting to suggest that it shrinks existing tumours. Because the tumours were advancing fast, and my vet found Lizzie to be otherwise healthy, I took the difficult decision to put her through surgery. I feared my independent-minded Lizzie would not last long once the tumours robbed her of all mobility.
Lizzie had her surgery 5 days ago, and I'm thrilled to report that she pulled through amazingly well. She's having to re-learn to walk normally, as the tumours had bent her hind legs outward and forced her to slide along on the inside of her legs. But she's made good progress and is already walking quite normally, especially on the left hind leg. She acquired mild respiratory symptoms following the surgery, but antibiotics seem to be keeping a lid on these.
Lizzie is one tough cookie, and she serves to remind us that age only tells part of the story. But this sure was a nail-biter.
Thanks again to all who offered wisdom, help and kind wishes.