Well, my other thought is that she seems extra-simple, presumably because she's a chimera and only has the limited intelligence and awareness that they raised her with. Therefore she blindly did whatever she thought was good without understanding or realising how much her actions worked against Athy and not knowing what to do about anything.
(And, perhaps, too, even though Claude loved Jennette, he didn't have the degree of intense love/hate he had/has towards Athy because of Athy's mother - not quite enough love for Jennette and too much loathing of Athy.)
Either way, I agree that she's not set up as a particularly likeable character from a reader's perspective.
unpopular opinion maybe?? but I can't stand jennette, judging by the way claude treats athy, she could have done /something/ to help athy in her last life. How can she be a kind person if she just let athy live such a horrible life in her shadow like that? It's not like athy was really evil or anything in her last life either...
Athy is so kind to her in this life, even though jennette "caused" her death in her last life; which tells me she's far more deserving of claude's love than jennette is.