| | Re: Am I taking this too far?
If it is a deal breaker, it is a deal breaker. Why question yourself about something so basic as the number of kids you want to raise? She can find someone who wants the same, or do it on her own (yes, she can--esp. if she goes through foster care and is willing to adopt children with special needs).
Never feel guilty about knowing your comfort level. You cannot commit to her knowing you have such an essential difference, and it would not be right of her to hold you to your promise in the light of such a difference. Better to part now. Especially since she seems unwilling to compromise on other issues--this isn't one to compromise on (if she knows this is what she wants), but certainly she should be capable of some compromise if she values your role in her life.