I don't find it difficult at all, as you stated her interests align very solidly with ours (as long as we are good a good ruler to the elves, which I intend to be), and what she did, she clearly did it to save her people and not out of any personnal thirst for power (her taking her secret to the grave when you kill her show that). And the only plot she made (that we're aware of, of course, she likely bloodied her hands much more than that) which I actually disapprove of is killing Cass' mother.
A very smart, very powerful elf whose main goal is getting us and keeping us in power as long as MC do what I'm naturally inclined to do? That's not the kind of help we can afford to reject. Only thing is that I'd REALLY like MC to insist with her on more transparency on her plottings. Well, that and have a discussion about Celestine's faction fucking up any of our future efforts to end the mistreatements toward elves.
Doesn't hurt that she's hot (tho I prefered her more regal appearance in first episodes).