She will gladly kill us the next morning, I doubt the words "I like you" will convince her. This would be even more inconsistent than the whole evil path of this quest. Girls like her prefer actions, not mere words.
Yes it is. But I want the main character to answer what he really thinks, more realistic. She may be amused by this, but words can be backed up by action.
In order for Minthara not to try to kill us, I would suggest destroying the Druid Grove alone, using only the forces of our party.
After that, she will at least be afraid to betray us and will warn about the decision of the absolute in advance, immediately moving on to the conversation about the fact that she does not want this in the morning after the party (without trying to kill), and will offer help on the way to the Moonrise Tower.