I asked myself the same question after reading her new lore!! I'm happy that i was not the only one confused haha. Well, from her new stories i get three main things:
1) Ahri is an addict. An addiction is defined as "a disorder characterized by compulsive engagament in rewarding stimuli despite adverse consequences", in Ahri's case these consequences are: psychological stress manifested as guilt, low self esteem (hating herself/what she is); feeling that she and/or her magic gets weaker (this is more tricky, i personally think this is psychological too because she was completely fine before stealing "essence" for the first time so she doesnt really needs it, but if her body gets so used to this "essence" that it's "unable" to function without the stimuli, then it can be physical aswell); and social difficulties (having a hard time interacting properly with others without wanting to feed from them, feeling that she is not worthy of bonding with others, and the risk of killing others around her during a relapse), so...seriously, she is sick!!
2) Ahri accept the fact that she is sick. Luckily, she recognized that she has a problem (unfortunately in a hard way) and want to get better. In her bio we are told "No more would she rely on borrowed memories and unfamiliar dreams", so it looks like she wants to learn to live her life without the aid of stealed "essence" (her drug), we can even link this to a real life example: an alcoholic that don't want to rely on drinking to have fun or be happy.
3) Ahri wants to know about her origins. Unlike other vastayan, Ahri didn't have the luxury of having a tribe, sure, she is a vastaya, but she was raised by foxes and learn things on her own or by stealing memories, so she has a desire to know where she came from and if there are more people like her who can help her to fully understand herself.
So, from point 1 and 2 i don't know why Xayah would hate her for "betraying her heritage", i mean sure ahri is an addict but she wants to change, and that's a good thing because by being sick she is dangerous to herself and others (that includes other vastaya!) so if anything Xayah (and everybody) should encourage her to change, especially since Ahri's dislike for her own nature (the only thing i can think that can annoy Xayah) is caused by the psychological stress stemmed from her addiction so she can't start to accept herself until she is cured...Then, from point 3 it make even less sense, Ahri is searching for her people (her people being vastayan) so she is trying to embrace her heritage...something that Xayah (a vastayan elitist) should be proud of!!
In the end i think that we can conclude that maybe (as @GreenLore said before) the stories are only a part of Ahri journey and she eventually will want to become human and her interaction with Xayah ingame reflect that future or...Xayah is just a jerk.