How do we feel about Therkla?

[Themrys]

Like I feel about Gilda in “Rigoletto.” Entertaining, but not as progressive as perhaps the author hoped. She was a character designed to die for love, so we could see how it affected some man.

Pretty much this.

She did have potential. A conflict between her loyalty to Kubota (in a society where honour and loyality can be a person's entire morality concept) and her conscience would have been very interesting.

I feel like she might have been a test run for the plot arc that will eventually be given to the Monster in the Dark: Raised to do evil, by an evil master, but redeemed by having met a truly good person.