It's mainly because of how she was presented in her first appearance: http://www.drowtales.com/mainarchive.php?sid=6037 In chapter 19, all Nidra look like rabid dogs, and she was the only effective one who appeared in later chapters (and is still alive). So I guess I got stuck on her as "preferred target". Plus, she has received no characterization: she only appears to wreak havoc or disrupt or foil other people's attempts. Whenever she appears, my problem-solving sense starts tingling.

About attacking Sillice, Sillice is like a crazy aggro generating machine, you can't really hate someone for attacking her, it's in the nature of things.