Might be a way around this that I missed, but after having completed Amelia's new quest and bought her, it seems to be impossible to get married. Since one of the marriage quests requires you to talk to the Servant's guild, which you can no longer do, can't progress it at all.

Did try talking to Amelia at home, but she seems to be permanently stuck asking that question about whether you prefer her or Ana, which seems odd in itself. I would have thought she'd at least have menu to repeat sex scenes like Daisy/Cali do.