This is new to me. I've had my male for over a year now, got him when he was 3 years old and have used PAM from day 1 with no noticeable negative symptoms. And I've had my female for several months and she's only about 2 years old and again, I've used PAM from day 1.
I'd ask the breeder for more information about the sensitivity. And as others have said, ask why you weren't at least warned about it.

I'm sorry about your loss. Every experience you have no matter how small and short it was is knowledge for the future and for friends {both animal and human}. Don't beat yourself up over the loss. Just remember the little girl: the joy she brought, and the lessons she taught.