Basically the game portrays her as someone who isn't exactly inherently evil; the drow lady is simply a broken person, who due to upbringing and her personal history became a tragic villain. She tries to play someone "strong and powerful", a being who does not display any weaknessess. This is just a ruse, which we learn only if PC chooses to side with Goblins.
And how exactly do we learn this? If a character is capable of feeling fear and can feel sadness due to loss they are not strong and are tragic and broken? Strong are only those that never feel fear and dgaf about anything?
No worries, I will explain.
Look at drow society. Displaying any kind of emotions is seen as weakness there, since it can be exploited. We do learn that she is full of fear and she tells us, although in anger,(we can presume that she tries to bluff us) we are told, that she uses the fear to strengthen herself (So she is ashamed of the feeling and in her eyes, it makes her weak, in her opinion). Which is clearly against what we get to learn via mind-reading.
She is tragic and broken person, because of both from where she comes (no, don't tell me that drow society is good in any way, according to lore almost everyone is insane there) and since we are told that she lost lots of family members, lovers and friends -> someone, her enemies I guess, killed them (it's also hinted that she did care about them, unlike typical drow). On top of this, her entire life is to quote the game itself "anticipating knife in the back".
The transformation of her behavior is also a kind of hint, towards who she really is.
There is very little of what you could call a good or happy life there. Struggling to survive every day is completely opposite of that actually.
In a short summary: In her eyes, being cold, uncaring, fearless etc. is seeing as being strong. That's what they basically "teach" the drow in Underdark. But, looking at how she acts later, I really question that she believes this without any kind of doubt.
If you have any further questions, feel free to ask; I reloaded basically every time I had a dialog with more important NPCs (Kagha, Halsin, etc.) so that I could learn more about them.