Here is the justification that I presented to Ush,
1) She attacked us first, we were acting peacefully and she, without warning, attacked back. We are thereby justified in attacking her, as she has been hostile towards us.
2) We have seen her use the dark side for her own ends. She used it to attack us, and it is therefore reasonable to suspect that she is using to keep control of the planet.
3) It would be beneficial to us to have a leader in place on Thalos who is not hostile to us, in case we ever have to go back. (Which, if the SnK is ON Thalos....Like my theory suggests..)
4) She is clearly a bad/evil politician, and there is some justice to removing an evil politician.
5) (and here is where it gets a bit squirrily.) We are, kinda, doing the will of the Force. Aquilla has seen a prophecy in which the jedi overthrow her. Now, in knowing about this prophecy she has become excessively fearful, which lead her to attack us. This act hase caused us to act, or want to act in a way that fulfills this prophecy. Hence, the doing the will of the force thing. However, interesting tidbit to think about, if Aquilla had never known about the prophecy, would it have come true? I would say no. as her actions are directly caused by her knowledge of this prophecy. So we can be seen to be doing to will of the force in fulfilling this prophecy, albiet in a rather circular and odd way.
Now, concluding, each one of these reasons alone would not justify us in attacking her. However, when they all are combined, I feel that we are not only justified, but would be acting from a sort of necessity of justice to help Thea. We, being Jedi, are compelled to do what we believe is good, and help spread peace and justice. Is Thalos now a justice and peaceful place? I would argue that it is not. Would instilling Thea as a ruler create this peace and justice? It is hard to say, but I think there is a higher chance, than without her. Because we believe this, we must see if there is proper justification for violating our non-intervention stance, and based on the points raised above I feel that there is. Only in these circumstances are we justified in taking the proposed actions. We are not revolutionaries, we do not desire to go around starting coups in all the places we do not feel there is enough justice. But when enough lines have been crossed, and enough evidence has been presented, we are compelled to act.