Just about the circumcision thing... I come from Europe where pretty much no guys were (only the Jewish ones) and then moved here in North Aerica where pretty much all guys my generation are. So I've experienced both.
When you're erect, I honestly can't say it makes a difference as far as I can tell. Hell, there have been time I didn't know if a guy was circumcised or not because I saw him erect first, until I saw him non-erect. So no, I can't imagine it makes any difference in conception.
It seems to me she just wants him to be the father. And I don't envy your situation at all, it sounds really horrible, but I'm afraid I don't have any advice for you... Just my support... And telling you that trying to make you feel bad about your penis is BS. One isn't better than the other, I mean, I can understand liking one better than the other I guess but it's not something you can help or anything so at this point she's just being mean on purpose in my opinion.