Also...wtf? Ayano never milked before... Author's on some bad drugs... And the excuse is BS...he's been stimulating the other girls' nipples just as much and none of them are laclactating
1) She's the randiest person in the dorm by a long-shot, order's niche porn in Shota's name, and says she only likes him for his dick. She probably teases her own nipples more than the other girls
combined.
2) I imagine individual hormones also play a role, so even if she wasn't constantly self-stimulating she could simply have a constitution that lends itself to lactation.
3) It's a sex-comedy manga. Some suspension of disbelief is required.