I don't see any selfishness here. You've supported your partner through health issues, you're willing to move to the other side of the world because it's her dream and financially support her while she finds work there (not always easy, I have to say - and the cost of living in Australia these days is utterly eye-watering compared to the UK) and after always agreeing you never want kids, she's now saying you aren't being compassionate for not wanting to contemplate it.
Kids alter everything. They're all-encompassing and all-demanding. And as she's 43 now, won't be finished with surgery for another 6 months or so if you factor in full recovery, and you'd presumably need a donor and very possibly IVF, you're looking at a timescale that makes conception really unlikely anyway. I do think that as a married couple you do need to discuss things, but I also think your frustration is completely understandable because really, thinking a child is an issue you can compromise on is barking mad. You both need to be on board because it is so unfair on the child if you aren't. And while as a society Australia is child-friendly, as a state provision system, not so much. They didn't even have mandatory maternity leave until I believe this year, for a start, and it's brief. They offer very good support for disabled people and education, and the healthcare is great (albeit partly dependent on compulsory, subsidised insurance, and with a co-pay) but if you were looking at being parents, this country is going to be a better place for the first couple of years, certainly as UK citizens. Has she even contemplated what the birth would cost, given the health insurance levels you'd need, especially at her age? And what is the legal position in Australia for gay couples who have a baby together? Here, both parents go straight on the birth certificate if you have a civil partnership. Over there, would the non-bio mother's role be recognised legally in any way at all? As far as I know only ACT is allowing gay marriage, which Abbot will challenge in the higher courts... and what rights to parentage does that convey? Finally, what on earth would it be like, having a first child so far away from all your support systems - family, friends, familiar culture?
It does sound as though you need to talk it through, because she hasn't even thought it through. It's a visceral desire for a child, and God knows I sympathise with that one - but not when nobody else's interests are being considered at all, and nor are the practicalities.