Nonono - I believe that you handled it the right way to. A direct confrontation would just get their back up and dig their heels in further. Taking off-topic opportunities to bring up sound reasons why animals shouldn't be bred is the best course of action. If you can it might also help of you phrase these things in ways that force her to agree with you ie: don't you think it's just terrible how many animals are euthanised in shelters every year? Don't you think it's wonderful how this or that organization is raising awareness about spaying and neutering pets, doesn't it break your heart when you hear that x shelter has x many puppies needing homes, etc. Get her subconscious on your side, and hope that it reaches her consciousness before puppers goes into heat!

You're not a coward - you're just not the kind of brave that's synonymous with reckless is all!