I do think a plan of action re other allotment holders might be wise...
Are you good with cake @YaMuvva or could you turn up bearing foil wrapped gifts of sausage and bacon butties one nippy morning (or a morning sausage-inna-bun bbq?)... As PP said, once they've accepted your foods they are going to find it far harder to be on Babs side...
Maintaining a pleasant, cheerful and interested presence could work wonders...be all sympathetic, 'yes it IS a shame but I wonder why Babs didn't offer to buy it when Sally sold the house? Ho hum...' etc etc! and 'Well.. perhaps you could share your plot with her?'...