[Ruchira Datta, Pam Korda, Carolyn Fusinato, and Roy Navarre as the Lanfear Pin-up of the Month Club]
Lanfear presents a bit of an enigma. Many of her actions have led some people to believe that she is not 100% Evil. The argument is that she and Beidomon drilled the Bore into the DO's prison by accident, and only became Forsaken after that either due to the DO's direct action, or out of pride. Moreover, everyone would link her with all the DO's ravages that followed, thinking she released him on purpose, no matter what she did. Being an extremely proud person, it would be hard for her to admit that she had just made a colossal mistake.
EVIDENCE: In the "Eyes of Charn" sequence [TSR: 26, The Dedicated, 303-6], Charn perceives Mierin as a good person, and maintains this belief even after she became Lanfear. Up to TFOH (see refutation), it can be claimed that she hadn't done any inarguably evil acts. She has been deceptive-- but what would one expect from an Aes Sedai? She is jealous and possessive of Rand-- but note that she had not done anything to harm her competition, which would probably be very easy for her to do. (She met Egwene in Tel'aran'rhiod, if I recall correctly, but anyway Egwene had been eliminated from the category of "competition" by this time.) She told Ishamael in TDR that she was loyal to the Dark One and no other. But in TSR, she suggested to Rand that they supplant the DO together. As for the scene at the end of TFOH, she was insane and not responsible for her actions. She dislikes being called Mierin in the extreme. This could be taken several ways. One way to take it is that she wants her former self to be disassociated from her current evil ways-- she does not want to be reminded of what she once was, it is too painful.
REFUTATION: I have always believed that Lanfear was evil, starting way back when we first meet her as Selene in TGH. She made my skin crawl. LTT, who even the Forsaken admit was an "honest man," said that Lanfear, even when she was Mierin, loved power more than anything else. What is the DO but the ultimate temptation of power?
All of her actions in "helping" Rand have not been to further his cause against the DO, but to gain his trust and lust, so that she could control him. She does not love Rand/LTT; she wants him to be her obedient lap-dog, and to serve him up on a platter to the DO, so that she can be the most powerful of his servants. She would supplant the DO AND the Creator in a second if she could, and then be disappointed that she wasn't powerful enough. Having deceived Rand for so long, it would have been simple for her to deceive Charn, a follower of the Way of the Leaf. (It is obvious from looking at the Tinkers and the Ancient Aiel that Way-of-the-Leafers cannot believe that the world is a Bad Place with Bad People in it.)
But anyway, evidence in TFOH closes the case for good. I do not refer to the skinning of Kadere, torturing of Egwene and Aviendha, killing of many bystanders, and attempted killing of Rand, although that provides plenty of evidence in itself, insanity or no. I refer to Moiraine's vision in the Rings of Rhuidean. [TFOH: 53, Fading Words, 637] If Moiraine had not jumped Lanfear, and let her have her way, Rand would be a) dead, or b) Lanfear's love-slave, with the crippled mind of LTT. These were Lanfear's plans. They are not the plans of a good person.
Oh, and if you need further proof, recall the ecstasy with which she describes bathing in the DO's presence at Shayol Ghul. She LIKES it.
Note that Lanfear did NOT send the Trollocs who fought Sammael's Trollocs in TSR. They were sent by Semirhage, on order of the DO. The DO, it seems, has been giving Rand aid for some time now, probably in the hopes of eventually turning him to the Dark Side. Any "help" Lanfear has done for Rand was probably in view of this end. Taking credit for rescuing him is certainly not past her.
Carolyn F. adds, that in a letter she got from RJ, he said that Lanfear was fixated on possessing a man who never loved her. (I guess LTT was just using her for sex, eh?) Her desire for Rand is as much desire for power as for him personally. She could get her hands on the remote-control ter'angreal for the kick-ass sa'angreal and get credit for turning the Dragon Reborn over to the DO. She wants power for power's sake, not for Rand's sake.
Finally, Cyndane's POV in [WH: 35, With The Choedan Kal, 649] clearly indicates she wants Rand to die. (Cyndane is Lanfear; see section 1.2.4.)