I'll add my voice to the well read and wise sages whom have already done so here.
Ah Elena! She is beautiful and after her life's end she becomes a servant of corruption. How Indeed? It's easy for anyone to lose sight of how a High Lord of the land, equipped with a Staff of Law, an artifact that was lost since the time of Desecration, could be undone. For that we must search the recesses of lore.
To look and understand the servant we must first delve into the master. What do we know about Lord Foul the Despiser and his methods? We know that he manipulates others and makes servants of the land destroy what they once loved. There are precidents for this:
In "Lords Foul's Bane" for example:
Covenant needed time to comprehend what had been done to Llaura. Her plight numbed him.
First she had been given knowledge which might have saved the Lords--and then she had ben made unable to communicate that knowledge. And her struggles to give the warning only ensured her failure by guaranteeing that the Lords would attempt to understand her rather than ride away. Yet what had been done to her had been unnecessary, gratuitous; the trap would have succeeded without it. In every facet of her misery, Covenant could hear Lord Foul laughing.
Ch 17: "End in Fire"
In "the Illearth War" we read:
"It is the Despisers way. In the battle of Soaring Woodhelven-we are told-he damaged the Heer Llaura and the child Pietten so that they would help destroy what they loved."
Ch 14: "Runnik's Tale"
In "The Power That Preserves" We read how the Giants were also turned. The three giant sons that had been given by birth to Wavenhair Haleall and Sparlimb Keelsetter had been the Giants hope.
"They saw the portent of their hope of Home--the three brothers--changed from fidelity to the most potent ill by one small stroke of the Despiser's evil. Who in the Land could hope to stand against a Giant-Raver? Thus the Unhomed became the means to destroy that to which they had held themselves true."
Ch 17: "The Spoiled Plains"
I'll mention also an important theme which is spoken by Foamfollower in LFB (and IMHO true in real life as well.)
"But hate, hate corrupts. I have been too quick to hate. I become like what I abhor."
Ch 21: "Treacher's Gorge"
This late quote is the crux of how Elena was turned. You mentioned
i know about the "apocolypse" in her stare
but perhaps you did not realize the significance.
Though the gaze was not not directed at him it bored through him like an auger. When it was gone it left a bloody weal across him.
It was the look of an apocalypse.
He could not think of any other namde for it but hate .
TIW Ch 22: ""Anundivian Yajna"
By the act of hate any person can become open to the forces they abhor and risk becoming the very thing they hate or seek to destroy.
Clearly Elena did
hate the Despiser. Her methods though were flawed (much like she was), perhaps even insane. For example she admired High Lord Kevin to the point of idol worship.
"Thomas Covenant, I believe that there is immeasurable strength in the consummation of despair-strength beyond all conceiving by an unholocausted soul. I believe that if High Lord kevin could speak from beyond the grave, he would utter a word which would unmarrow the very bones of Lord Foul's Despite."
"That's madness!" Covenant gasped thickly.
Ch 21: "Lena's Daughter"
Here she spoke her true intentions as to how she would, if she could, destroy Lord Foul with the power of the Seventh Ward.
Then when she found, through Amok and the unwitting Bloodguard "The Power of Command" also known ans the Seventh Ward she bent down to drink deep of "The blood of the earth" and called dead High Lord Kevin Landwaster to do her bidding. Here was her ultimate folly and mistake.
Kevin's ghost left as he was commanded to do by Elena's compulsion to fight with Lord Foul. he returned however defeated and mastered.
"Fool!" he cried in a paroxysm of anguish. "Damned betrayer! You have broken the Law of Death to summon me-you have unleashed measureless opportunities or evil upon the earth-and the Despiser mastered me as easily as if I were a child! The Illearth stone consumes. Fight Fool! I am Commanded to destroy you!"
Ch 25: "The Seventh Ward"
Ah Elena.....
Eventually she was destroyed by Kevin and made to serve the Despiser after she died, as a spectre or ghost if you will, mastered like Kevin was, by the Illearth Stone.
but does she still have feelings for covenant in TPTP? any help, especially info from TPTP would be much appreciated. thanks guys.
This sounds to me like something of a spoiler perhaps I don't know but i'll let someone else tend to that part of your question.