Okay so foxes are known to be mischievous and tricky towards other people right?
As what we can see here, Ladybug asks for the fox miraculous back because Master Fu ordered her to do so
(do you get it people? pls stop blaming/hating on mari for that)
And Alya hesitates, because being a superheroine is what she wanted, plus, she newly formed a bond with trixx.
And when Ladybug left/hid herself, trixx then begins to tell Alya how she’s fit to be a superheroine then all of the sudden, Trixx bursts out the word “Trustworthy”
Now let me tell you my perspective, kwamis aren’t dumb, they know what’s up (but sometimes they just don’t show it to other people) So what if Trixx is testing Alya to see if she is worthy enough to hold the fox miraculous and to see if she’s trustworthy of holding one of the miraculous? It could be Trixx tempting her to test her, who knows? Foxes aren’t predictable after all.
And just after she heard the word “Trustworthy”, she made up her mind to keep the promise and return the miraculous.
But I don’t think that’s the end of Rena Rouge. Why? Because of this scene.
This scene may prove that Alya is fit to hold one of the miraculous (specifically the fox miraculous). She holds on to justice and keeps her word, someone Master Fu is looking for when giving out miraculouses. I don’t know, I may be wrong but I have a strong feeling Trixx and Alya are going to meet up soon. Maybe Master Fu will give it to her himself after he studies the book. All I’m saying is that this girl deserves the fox miraculous. That’s that.