*imitates a goblin voice* Wait a minute.. huh.. what??
While I am undergoing a new extensive playthrough with Minthara now not once have I ever triggered any of those lines for Minthara, only having done so for Karlach related content when I romanced Karlach extensively and other active team members would have a say while out on the road after the Act relevant romance scene took place but it would be inconsitent and out of blue and not a guaranteed to happen moment.
This gives me hope that there will be two more romance scenes for Minthara in the future, maybe thats one reason I just never seen or managed to have these triggered because.. well... what romance scenes?? None currently exist for Minthara in Act 2 and Act 3, there is no structure for those lines to take place in.
(edit) Check this out, you can hear the VA delivering the Minthara lines.