> I understand that there is an increased risk of mammary cancer in unspayed bitches
This is apparently true but the study done to give this info was small and I believe the animals were not diverse in breed or relationship.
Also half of mammary tumours are benign.
Of the six related bitches of one breed I have owned, and one of another breed who had more than two seasons only one ever had a mammary tumour (carcinoma) which was spotted easily and removed at pea size when she was 5, it did reoccur in same location some few years later and the gland was removed (partial mastectomy), she lived trouble free to 13 1/2 years and her death was not cancer related.
If the statistics are to be believed I should have had at least 3 of mine with tumours of which half would b e benign
The risks have to be taken on balance. No-one suggests that women should all have hysterectomies to reduce breast cancer, as we all know that having a hysterectomy can solve some problems but cause others.
Maybe print off this balanced article to help her and also to show her Vet, to stop him being a bully.
http://www.naiaonline.org/pdfs/LongTermHealthEffectsOfSpayNeuterInDogs.pdf