I think this is a decision that is TOTALLY up to you, and don't be pressured by all the current "you must spay/neuter" type stuff, bc it's not true that you must do it. The most important thing if you don't spay is to fiercely protect her from male dogs, and it sounds like you're already diligent in doing this, so that's the main thing. Yes, spaying females can decrease the incidence of certain health issues, but still, that doesn't mean you must spay. MANY female dogs live their lives unspayed and live long, healthy, normal lives...just like us unspayed human females do
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