What a sad story
I completely understand why you’d want to rescue her.
I’ll admit, when I read the title my first reaction was “probably not”. But reading the full story I understand why you’d want to try. The fact that she was bonded before as an unspayed lady makes me think she might just bond easily. But I think the real issue is how your current buns will react. Did they bond easily?
She also might not be too old to be spayed…I think some vets have 6 as their cut off, and my local vet has neutered buns as old as 9. So might be worth calling around to see.
I think if you confirm she cannot be spayed, i might try bringing her home and seeing how your pair reacts to her presence in the house. Don’t actually introduce them, but if possible set her up in another room and see if your pairs behavior changes.
If your buns start acting weird , then there prob isn’t a chance of bonding them properly unless she is spayed. But if everyone is chill, then maybe it could work?
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.