@Kyto1984,
@catislong
This is just my conjecture, but I think Ai Fa's issue is not against motherhood itself, it's more like "I don't want to marry into another clan and abandon my own Fa clan". It's also possible she doesn't see herself as a good mother; she performs well activities that culture considers masculine (as giba hunting), but she sucks at feminine stuff like firekeeping.
Neither of those issues would apply to a hypothetical marriage between Ai and Asuta; he doesn't belong to a clan so they'd be still under the Fa clan, and he's fine performing all those "feminine" activities Ai doesn't.
On not showing any romantic intention: after rereading ch.12 I've noticed how bad Ai Fa is when it comes to express herself and her emotions. It's possible she isn't even aware she's becoming more and more romantically inclined towards Asuta, but that progression is clear when you reread the chapters so far.