"Just one litter" -- We had that thought too when we first got Star, we were so in love with her - but my vet convinced me it was far better to spay her before having a litter. I'm glad we did. When we decided to add another dog, we adopted from a shelter. It was March, and they were literally overrun with "Christmas litter puppies" that weren't adopted. There were cages that had as many as 8 and 9 puppies all crammed in together. Rosie had been part of a litter of 7. She was only the fourth to be adopted. I often wonder how many of those "adorable puoppies" made it to a home? Seeing that was enough for me, personally I think only serious breeders should be the only ones to breed their dogs. When we adopted our third dog, Sherman, his breeder (professional breeders) She said their philosophy is that THEY were responsible for bringing these dogs into the world, THEY were willing to be responsible to that dog for its entire life, and made it clear that he would ALWAYS be welcomed back FOR ANY REASON.
I hope you don't loose a friendship over this, and i admire your efforts to show her the other side of puppy breeding. I hope she'll listen.