See i'm gonna agree and disagree, but it will most certainly take forever to write this(maybe read too) cause i've gotta find episodes...so bear with me.
The Best, most simple way to do this is simply 'chart' Cordelias on-screen journey.
Let us start at the beginning, way way back nearly a decade(where has that time gone?) ago, when Miss Cordelia Chase first graced our screens.
In 'Welcome to the Hellmouth', we are introduced to a character, one of simple dimensions, that we shall call Cordelia 90210. Rich socialite with a gaggle of 'friends', emphasis on the more expensive things in life. She is quick witted, often bullying, rarely without a condecending comment towards those she deems inferior to all, this girl is pure 'Class'.
She has little time for plebs, because she is an 'It' girl of sorts, what she says, 'It' is 'law'.
However, this is called into question by the arrival of someone, someone who Cordelia initially takes under her wing as someone she could be seen with, but then drops faster than she'd drop an ounce after a Christmas of excess in Aspen. This is Buffy Summers.
Buffy and Cordy are opposites of each other.....or so we are lead to believe.
We know that in a past life, Buffy WAS Cordelia, that sans some Mythic Intervention Buffy would still be this girl, this woman. In the magnificent 'Out of Mind, Out of Sight', we see Buffy come to a certain realisation about Cordelia, which is exactly when we come to it too.
These two women are more alike than we knew.
They have a Burden of responsibility, one that they cannot pass to anyone else, one they must at the end of the day, bear alone.
One is Slaying and Fighting the Demon the Other is maintaining the Social Equilibrium, keeping the Order of things which help grease wheels of the societal norms so things run (as much as possible) smoothly.
By the end of this episode we are left with no doubt that there is more to Cordelia than meets the eye. She isn't just the selfish, money and status seeking girl we thought we knew.
By the End of Prophecy Girl we see this Cordelia erupt ever more to the screen.
She is in a relationship with someone and is losing some of the control she holds dear, giving into emotion, to feeling. She feels she should be annoyed that she isn't actually annoyed at behaviour shown. However, something truly terrible happens to this relationship that puts on hold this burgeoning evolution and, with the exception of the helping at the Library of PG, next we see of Cordelia she is pretty much the girl we first met.....except a little more adult. In 'When She was Bad' we get to see Cordelia give Buffy, who is now playing a party girl(Faith?), some sage advice, something we would not have seen pre-'OOM,OOS'. She doesn't stay like this for long, but long enough for us, the viewer, to see a positive shift in the way this girl is growing and expressing herself.
We have moments over the next few episodes of this differing Cordelia, but the biggest shock to come happens in the 'Whats my Line' double.
Shock Horror, Cordelia Chase kisses Xander Harris. He is everything she doesn't want in a man. He is poor, unpopular with her friends and dresses extremely bad, but she sees something in him. She sees that though he is ALL of these, he is also someone who 'fights' for his beliefs, for his friends and thanks to the demon stuff, for just about anyone.
She sees this because they are constantly put in these situations where Xander is forced to step up, even though he has very little chance of doing anything.
This then draws out another visible change in Cordelia. by the season 3 episode 'Anne', Cordelia is a fully fledged member of the Scoobies, a group by all rights she should avoid like the plague. She even enjoys to an extent the safety of this group, the fact she can be with them and not put on the 'Cordelia 90210' persona that she must don every day.
However, this is taken away from her because of the events in 'Lovers walk'.
The fact that Xander Harris, this guy she has sacrificed so much for, could betray her with someone she feels a certain superiority over in everyway she feels is still important to her, puts the new changing Cordelia on hold, reverting back to our original version.
This Cordelia stays with us for most of the rest of the season, until we learn that Daddy has lost everything. The one person Cordelia doesn't want to learn this, is the one person that does, Xander.
Even through everything these two have endured, the new bout of ridicule she has suffered and exacted on him even, he still holds her secret. He even does something honourable for her without need of some form of recompense.
Part One of the Cordelia Evolution over...Part Two coming soon😉...LOL(actually i'm just tired)
