Summary : Lila still hates Ladybug but befriends Marinette to have more clout in the school and Marinette tries to help Lila discovering she's a victim of neglect but also countering her manipulations. In the end they end rivals. More details are : Lila making Marinette fight more with Kagami and Chloe, Marinette saying Lila can come to her everytime she feels lonely because of her absent parents, Lila pushing Lukanette to get rid of Marinette as a love rival more easily, Marinette being more bold and confident thanks to Lila, Lila getting close to Gab then discovering his identity thanks to the rings. Finally Lilanette breakup as Marinette cannot tolerate Lila's lies anymore and the reveal of Cerise.
First the point of divergence :
At the end of Volpina, Marinette catches up to Lila as she's about to leave the school to go to on a travel with her mother who's a diplomat and introduce herself as the class president and that she hopes to become friend with Lila when she comes back which Lila accepts we have a flashback on her side of the class praising Marinette except Chloe of course which means she's a valuable connection.
Season 2: goes the same or you can put the event I will put in Season 3 here it doesn't change much. I will change the finale by introducing the fact Lila is often home alone as her mom is a diplomate and an ambassador for different organizations which means she's rarely home and her husband is "missing". Lila is often left to the old lady nearby who doesn't really care about her as long as she sent her a text to tell she's alive.
Season 3: starts with a two parters about Lila. The first one is about her becoming popular with everyone but being slapped down by Chloe who reveals that whilst Lila does travel and meet celebrities it's not nearly as grandiose as she makes it out to be with a lot of lies blended to the truth she contacts a girl who was with Lila in one of the photo that tells her a lot of mean thing about her ( I admit it's a bit of a retcon for Chloe to have a "friend" overseas but she's just a fellow mean diamond so it still makes sense ) Chloe obviously being jealous about Lila copying up to Adrien. Lila gets angry and Hawkmoth sends an akuma but she turns the table with a pity party on Chloe who almost gets akumatized due to Adrian and her classmates reaction but resists until Adrian takes her glasses and smash them releasing the akuma. Another person gets akumatized and is defeated. Lila learns of Marinette crush on Adrian by spying on a convo between her and Alya and decide to exploit this to make her and Chloe tear each other apart.
In the second part she enact a plan to pimp Marinette for Adrian triggering Chloe jealousy and bullying before convincing Marinette to retaliate Marinette accepts at first but realize she's too mean to Chloe and refuse to deliver the final blow to Chloe's rep that would also make her look cruel and superficial to Adrian. Seeing her plan fail so close to completion get Lila akumatized into Cameleon and bully Chloe under a Marinette disguise after being revealed and deakumatized she unleash a sob story about her resentment and fear of Chloe and ask Marinette in tear to forgive her which she does.
In another episode we learn more about Lila, that when her first mother is away she goes to a second "mother" a rich blind Italian lady who lsot most of her family whom she speaks in her mother tongue with. She blindly trusts Lila who unleash terrifying emotional manipulation for a 14yrs old, officially she works part time for the lady but she treats her like a daughter and thinks she's an illegal immigrant who lost her family and helps her. In that episode Marinette learns about how neglectful is Lila first set of parents as the lady who supposed to take care of her doesn't know where Lila is when Lila pretended to be sick to skip school triggering Miss Bustier to send Marinette with her homework. Marinette doesn't learn about Lila second mom but threatens to tell everything to the Lila's first mother triggering the old lady into getting akumatized to capture Lila. Marinette tells Lila she can come see her and her parents anytime if she feels lonely as Lila doesn't want her home situation to be known by the rest of her classmates. The ending I would leave voluntarily ambiguous does Lila really is grateful to Marinette or is she just earning pity points ? A bit of both I would say. Finally a last epsidoe where she helps Marinette beef with Kagami before their friendships blossoms in Ikari Gozen. She also clearly pushes in some episode Lukanette as a way to get rid of her rival without having to go through the trouble of breaking her friendship or pushing Marinetre to be evil to hinder her chances with Adrian
Lila is some season 3 other episode as a part of Marinette friend group sometimes countering sometimes helping an akumatization.
Season 4: same as season 3 but she has a hand in Adrigami breakup, tries to salvage Lukanette gets closer to Gabriel and Hawkmoth even going as far as to exploit her friendship with Marinette to get a mass akumatization under the guise of being threatened by a villain to do so before Lilanette comes to an end as Marinette discovers it's a lie and expose her with Lila in that Ladybug like episode having to choose between friendship and revenge and choosing the latter + cerise reveal.
Season 5 : she discovers who Hawkmoth is thanks to noticing the correlation between the number of rings and miraculous powers and getting herself akumatized to test it out recording everything on camera. She also use her power to get Miss tsurugi and Nathalie to tell her the truth. She steals Tusrugi tech at this time too by having Miss Tsurugi tell her the passwords and we see her come up with plans to steal the mirsculouses .