
There was a study I read about that stated the reoccurence rate of mammary tumours was not changed with spaying, so I would not bother having her spayed, but have the tumour taken care of.
My five year old bitch who had had two litters developed a mammary tumour, and I had it removed (it was pea size). It came back in same place some 3 1/2 years later and I had the gland and adjoining one on same lymph node removed. She is now 12 years old.
I did have her spayed at the time, as I thought it might help, but fortunately mine is a breed whose coat does not change too dramatically, unlike the Spaniel breeds.