I am definitely in the camp that she did not have a well thought out plan. I believe she was adapting and figuring it out as best she could alone. She wasn’t raised like the other three. Even Michael had Max and Isabel. She had no one. Then to be almost completely rejected by this family pushed her already barely hanging on by a thread human side over the tipping point,
I’m still building her story and I’ve been reading other fan fics I can find on her to see what else has already been done with her character. It’s a shame how more then a few portray her in such an awful manner.
Tess knew way more about the destiny and politics then the other three and because of Nacedo raising her she was more crafty by the environment she was raised. Really she is the most tragic character... raised by a twisted killer, rejected by her destiny, inadvertently (I believe also she meant no harm intended) kills a beloved person of said people she is trying to join, then the possible rejection on Antar. Complex character indeed.