Dixie,
I was talking with my friend, Robin, yesterday. She has been going back and forth on this same thing with her Maggie (who is Lilly's mother). Maggie has just had the one litter (14 puppies) and she was a terrific mother. Robin "knows" more now than she did then and was doing all the appropriate hip certifications at the urging of her vet. Maggie has arthritis, but perfect hips. She has made the decision, like you, to spay her. And it has broken her heart. I think it is the right decision, but completely understand the dilemma for both of you, since you have such beautiful, maternal girls.
Hope Dixie has a good day today. Report in when you can.
Logan