I'd say she qualifies more as an antihero so far because she hasn't actually done anything bad yet. (Being happy that she gets to kill her former bully is bad but only mentally, not in terms of her actual action.) If she actually does murder Miya then she will go over the line to villain protagonist, but it's pretty up in the air whether she'll actually follow through with that, especially since she actually seems to enjoy texting with Miya lol.
Except I'd say she has done bad things already. She's swapped her phone with Risa's in order to keep them apart and get closer to Miya with intent to kill. Doesn't mean she can't end up becoming an antihero, but currently I'm not sure she'll stumble down that path.
I think it'll be entertaining either way, whether she gets "reformed", reintegrates into society and accepts Miya or even comes to form a throuple with her and Risa, or (more likely imo) descends into becoming a subversive, destructive force. A character that not only would keep being bitten by a zombie a secret, but would deliberately sabotage a survivor group (sans Risa) to wipe them out. I think that much is teased already.