The first line and the interaction with player after the failed attempt to kill us in sleep tell us, in a obvious way, that she clearly does not like betraying others.
It doesn't come as easy thing for her. If she has done it before, which very likely was the case, as she is a drow; it wasn't out of her choice, or there was huge feeling of guilt left afterwards, combined with being really conflicted over what to do.
Then we got the fact that she dislikes Lolth, a goddess of betrayal, backstabbing and cruelty. Another hint.
Yeah, no one wants to kill people that they like, she has no problems with killing innocent people that she doesn't know personally though, there is zero hesitation or remorse on her part when it comes to slaughtering everyone in the grove. She hesitates killing the player because she likes the player, personally, it's like if you were a servant of the absolute and absolute asked you to smash your nice car that you like. You belong to her, remember?